Engineering topics

Keil, Lanny C.

Publications and source records attributed to Keil, Lanny C..

14 records

NASA NTRS1996

Drinking-Induced Plasma Vasopressin and Norepinephrine Changes in Dehydrated Humans

After 24-h water deprivation, five men (23-41 yr; 78 +/- 3.6 kg) consumed, within 4.0-6.2 min, 12 mL/kg of one of six fluid formulations (16.5 C) once a week over a period of 6 weeks: water, hypotonic saline (0.045% Na(+)), isotopic saline (0.36%, Na(+)), hypertonic glucose 9 7%, glucose), and two commercial mildly hypertonic 9.7% carbohydrate drinks. Blood samples were drawn 5 min before and: 3, 9, 15, 30, and 70 min after completion of drinking. Ingestion induced no significant change in plasma Na(+), K(+), osmotic, or protein concentrations, blood pressure; or heart rate. Plasma volume (PV) was increases (P <0.05) between 30-70 min with isotonic saline and the two commercial drinks. Ingestion induced a decrease in plasma AVP (PAVP) at 3 min, which was maximal (P < 0.05) at 15 min with all drinks. Thus, the act of drinking, independent of the composition or osmolality of the fluid absorbed, leads to a prompt inhibition of PAVP secretion in man. With the exception of rehydration with isotonic saline, this prompt response was followed by a long lasting inhibition of PAVP. There was no change in PRA, plasma aldosterone, atrial natriuretic peptide, or epinephrine, but an increase in plasma norepinephrine occurred immediately after ingestion, which suggests, like that for PAVP depression, a drinking-stimulate neural mechanism.

Geelen, Ghislaine↗

NASA NTRS1995

Intrapericardial denervation: Responses to water immersion in rhesus monkeys

Eleven anesthetized rhesus monkeys were used to study cardiovascular, renal, and endocrine alterations associated with 120 min of head-out water immersion. Five animals underwent complete intrapericardial denervation using the Randall technique, while the remaining six monkeys served as intact controls. Each animal was chronically instrumented with an electromagnetic flow probe on the ascending aorta, a strain gauge pressure transducer implanted in the apex of the left ventricle (LV), and electrocardiogram leads anchored to the chest wall and LV. During immersion, LV end-diastolic pressure, urine flow, glomerular filtration rate, sodium excretion, and circulating atrial natriuretic peptide (ANP) each increased (P less than 0.05) for intact and denervated monkeys. There were no alterations in free water clearance in either group during immersion, yet fractional excretion of free water increased (P less than 0.05) in the intact monkeys. Plasma renin activity (PRA) decreased (P less than 0.05) during immersion in intact monkeys but not the denervated animals. Plasma vasopressin (PVP) concentration decreased (P less than 0.05) during the first 30 min of immersion in both groups but was not distinguishable from control by 60 min of immersion in denervated monkeys. These data demonstrate that complete cardiac denervation does not block the rise in plasma ANP or prevent the natriuresis associated with head-out water immersion. The suppression of PVP during the first minutes of immersion after complete cardiac denervation suggests that extracardiac sensing mechanisms associated with the induced fluid shifts may be responsible for the findings. water immersion; natriuresis; vasopressin; eardiae denervation; monkey

McKeever, Kenneth H.↗

NASA NTRS1995

Intrapericardial Denervation: Responses to Water Immersion in Rhesus Monkeys

McKeever, Kenneth H.↗

NASA NTRS1992

The effect of head-down tilt and water immersion on intracranial pressure in nonhuman primates

Intracranial pressure (ICP) is investigated in primates during and after -6-deg head-down tilt (HDT) and immersion in water to examine the effects of the headward fluid shift related to spaceflight. Following the HDT the primates are subjected to head-out thermoneutral water immersion, and the ICP is subsequently measured. ICP is found to increase from 3.8 +/- 1.1 to 5.3 +/- 1.3 mm Hg during the horizontal control period. ICP stabilizes at -6.3 +/- 1.3 mm Hg and then increases to -2.2 +/- 1.9 mm Hg during partial immersion, and ICP subsequently returns to preimmersion levels after immersion. These data indicate that exposure to HDT or water immersion lead to an early sharp increase in ICP, and water immersion alone leads to higher ICP levels. A significant conclusion of the work is that the ICP did not approach pathological levels, and this finding is relevant to human spaceflight research.

Keil, Lanny C.↗

NASA NTRS1992

Effects of CSF hormones and ionic composition on salt/water metabolism

This collaborative agreement between Drs. Severs and Keil began in 1981, arising from a continuing interest in the issue of what, exactly, are the consequences of headward fluid shifts during manned spaceflight. Such shifts were recognized early by both U.S. and Soviet Scientists because of signs and symptoms referable to the head. Some of these include disturbed vision, puffiness in the face and periorbital areas, headache, vestibular dysfunction and distended jugular veins. We posited that the fluid shift had an immediate effect on the brain, and a long-term action requiring a neural interpretation of the flight environment. This would re-adjust both efferent neural as well as hormonal mechanisms to sustain cardiovascular and fluid/electrolyte balance consonent with survival in microgravity. Work along these lines is summarized.

Severs, Walter B.↗

NASA NTRS1991

Cerebrospinal fluid pressure in conscious head-down tilted rats

The acute effects of a 1-h -45 deg head-down tilt on continouously recorded cerebrospinal fluid pressure (PCSF) of conscious rats are studied in order to investigate the shift of blood volume into the thoracic cavity in microgravity. PCSF, evaluated in 15-min time blocks over a 3-h experiment, increased slightly (less than 0.05) during the first 30 min of a control hour at 0 deg. There was a transient increase for about 5 min immediately after tilt (-45 deg) that may have been due to head movement after the position change. PCSF was statistically unchanged (above 0.05) during the second (-45 deg) hour and the third (0 deg) recovery hour. It is shown that the dynamics of intracranial pressure regulation can accommodate the acute cephalad fluid shift after tilting.

Severs, Walter B.↗

NASA NTRS1991

Hormonal regulation of fluid and electrolyte metabolism during periods of headward fluid shifts

In the broadest sense, this project evaluates how spaceflight induced shifts of blood and interstitial fluids into the thorax affect regulation by the central nervous system (CNS) of fluid-electrolyte hormone secretion. Specifically, it focuses on the role of hormones related to salt/water balance and their potential function in the control of intracranial pressure and cerebrospinal fluid (CSF) composition. Fluid-electrolyte status during spaceflight gradually equilibrates, with a reduction in all body fluid compartments. Related to this is the cardiovascular deconditioning of spaceflight which is manifested upon return to earth as orthostatic intolerance.

Keil, Lanny C.↗

NASA NTRS1990

Intrapericardial denervation - Radial artery blood flow and heart rate responses to LBNP

The effects of intrapericardial denervation on the radial artery blood flow velocity (RABFV) and heart rate (HR) responses to LBNP in rhesus monkeys were investigated by measuring the RABFV transcutaneously by a continuous-wave Doppler ultrasonic flowmeter in order to derive an index of forearm blood flow response to low (0 to -20 mm Hg) and high (0 to -60 mm Hg) ramp exposures during supine LBNP. Four of the eight subjects were subjected to efferent and afferent cardiac denervation. It was found that, during low levels of LBNP, monkeys with cardiac denervation exhibited no cardiopulmonary baroreceptor-mediated change in the RABFV or HR, unlike the intact animals, which showed steady decreases in RABFV during both high- and low-pressure protocols. It is suggested that forearm blood flow and HR responses to low-level LBNP, along with pharmacological challenge, are viable physiological tests for verifying the completeness of atrial and cardiopulmonary baroreceptor denervation.

Mckeever, Kenneth H.↗

NASA NTRS1990

Corticosterone, but not Glucose, Treatment Enables Fasted Adrenalectomized Rats to Survive Moderate Hemorrhage

Fed adrenalectomized rats survive the stress of hemorrhage and hypovolemia, whereas fasted adrenalectomized rats become hypotensive and hypoglycemic after the first 90 min and die within 4 hours (h). We have studied the effects of glucose and corticosterone (B) infusions after hemorrhage as well as treatment with B at the time of adrenalectomy on the capacity of chronically prepared, conscious, fasted, adrenalectomized rats to survive hemorrhage. We have also measured the magnitudes of vasoactive hormone responses to hemorrhage. Maintenance of plasma glucose concentrations did not sustain life; however, treatment of rats at the time of adrenalectomy with B allowed 100 percent survival, and acute treatment of adrenalectomized rats at the time of hemorrhage allowed about 50 percent survival during the 5-h posthemorrhage observation period. Rats in the acute B infusion group that died exhibited significantly increased plasma B and significantly decreased plasma glucose concentrations by 2 h compared to the rats that lived. Plasma vasopressin, renin, and norepinephrine responses to hemorrhage were markedly augmented in the adrenalectomized rats not treated with B, and plasma vasopressin concentrations were significantly elevated at 1 and 2 h in all of the rats that subsequently died compared to values in those that lived. We conclude that: 1) death after hemorrhage in fasted adrenalectomized rats is not a result of lack of glucose; 2) chronic and, to an extent, acute treatment of fasted adrenalectomized rats with B enables survival; 3) fasted adrenalectomized rats exhibit strong evidence of hepatic insufficiency which is not apparent in either fed adrenalectomized rats or B-treated fasted adrenalectomized rats; 4) death after hemorrhage in fasted adrenalectomized rats may result from hepatic failure as a consequence of marked splanchnic vasoconstriction mediated bv the actions of extraordinarily high levels of vasoactive hormones after hemorrhage; and 5) B appears to act to decrease the magnitude of response of vasoactive hormones after hemorrhage in fasted adrenatectomized rats.

Darlington, Daniel N.↗

NASA NTRS1989

Potentiation of Hormonal Responses to Hemorrhage and Fasting, but not Hypoglycemia in Conscious Adrenalectomized Rats

Bilateral adrenalectomy (ADRX) in rats removes the source of two major stress-responsive hormones, corticosterone and epinephrine. To test how ADRX rats with-stand stress, we performed the following experiments in adult male rats provided with indwelling femoral arterial and venous cannulae and either ADRX or sham-adrenalectomized (Sham) 3 days later and given 0.5% NaCl to drink. Five to 6 days after adrenal surgery the rats were studied after either a 15 ml/kg.5 min hemorrhage or after an overnight fast followed by insulin-induced hypoglycemia. In fed unstressed ADRX rats, basal mean arterial blood pressure was slightly decreased; heart rate was increased; blood volume, vasopressin, and oxytocin concentrations were not different from sham values; and renin and norepinephrine were significantly elevated. The recovery of arterial pressure after hemorrhage in the ADRX rats was similar to that in the sham group over a 5-h period; however, the responses of vasopressin and oxytocin were significantly greater, and those of renin and norepinephrine were markedly potentiated in the ADRX group. Heart rate recovered faster in the ADRX group and was elevated, compared to the sham value, for most of the 5-h period. Restitution of blood volume was attenuated in the ADRX group, although the restitution of plasma protein was not different between the groups. A significant difference in the change in plasma osmolality between groups after hemorrhage may account for the attenuated restitution of blood volume. After an overnight fast, which reduced blood volume in both groups of rats, the plasma renin concentration rose still further in ADRX rats; the differences in other measured variables observed between fed ADRX and sham groups remained the same. The insulin-induced 50% decrease in glucose caused minor effects on arterial blood pressure and heart rate and occasioned responses in renin and norepinephrine of similar magnitudes in the two groups. We conclude that in the absence of the adrenals, rats restore arterial pressure after hemorrhage remarkably well through potentiation of the responses of other vasoactive neural and hormonal systems. In these studies the marked potentiation of the renin response suggests that the renin-angiotensin system may be important in the maintenance of arterial blood pressure after reductions in blood volume.

Darlington, Daniel N.↗

NASA NTRS1989

Lack of effect of vasopressin replacement on renin hypersecretion in Brattleboro rats

The congenital vasopressin deficiency in homozygous Brattleboro rats with diabetes insipidus is associated with elevated plasma renin activity at rest and supernormal responses to stimuli that increase renin secretion. The mechanism underlying this phenomenon was investigated by infusing homozygous and heterozygous Brattleboro rats with a dose of arginine vasopressin that restored plasma vasopressin to normal in the homozygous animals. The resulting data indicate that increased renin secretion in homozygous rats results from increased sympathetic activity. Because circulating vasopressin does not cross the blood-brain barrier, it seems likely that the increased sympathetic activity is central in origin.

Golin, Raffaello M. A.↗

NASA NTRS1989

Vascular Responsiveness in Adrenalectomized Rats with Corticosterone Replacement

To determine under resting, unstressed conditions the circulating glucocorticoid concentrations that best maintain sensitivity of the vascular smooth muscle and baroreceptor responses to vasoactive agents, rats with vascular cannulas were sham-adrenalectomized (sham) or adrenalectomized (ADRX) and provided with four levels of corticosterone replacement (-100 mg fused pellets of corticosterone: cholesterol 0, 20, 40, and 80% implanted subcutaneously at the time of adrenal surgery). Changes in vascular and baroreflex responses were determined after intravenous injection of varying doses of phenylephrine and nitroglycerin with measurement of arterial blood pressure and heart rate in the conscious, chronically cannulated rats. Vascular sensitivity was decreased, and resting arterial blood pressure tended to be decreased in the adrenalectomized rats; both were restored to normal with levels of corticosterone (40%), which also maintained body weight gain, thymus weight, and plasma corticosteroid binding globulin concentrations at normal values. The baroreflex curve generated from the sham group was different from the curves generated from the ADRX+O, 20, and 40% groups, but not different from that of the ADRX+80% group, suggesting that the baroreflex is maintained by higher levels of corticosterone than are necessary for the maintenance of the other variables. These data demonstrate that physiological levels of corticosterone (40% pellet) restore vascular responsiveness, body weight, thymus weight, and transcortin levels to normal in ADRX rats, whereas higher levels (80% pellet) are necessary for restoration of the baroreflex.

Darlington, Daniel N.↗

NASA NTRS1989

Paraventricular Stimulation with Glutamate Elicits Bradycardia and Pituitary Responses

The excitatory neurotransmitter, L-glutamate (0.5 M, pH 7.4), or the organic acid, acetate (0.5 M, pH 7.4), was microinjected (50 nl over 2 min) directly into the paraventricular nuclei (PVN) of pentobarbital sodium-anesthetized rats while arterial blood pressure and heart rate and plasma adrenocorticotropic hormone (ACTH), vasopressin, and oxytocin were measured. Activation of PVN neurons with L-glutamate led to increases in plasma ACTH, vasopressin, and oxytocin and a profound bradycardia (-80 beats/min) with little change in arterial blood pressure. Microinjection of acetate had no effect on the above variables. The decrease in heart rate was shown to be dependent on the concentration of glutamate injected and the volume of injectate. The bradycardia was mediated through the autonomic nervous system because ganglionic blockade (pentolinium tartrate) eliminated the response; atropine and propranolol severely attenuated the bradycardia. The bradycardia was greatest when L-glutamate was microinjected into the caudal PVN. Injections into the rostral PVN or into nuclei surrounding the PVN led to small or nonsignificant decreases in heart rate. Focal electric stimulation (2-50 pA) of the PVN also led to decreases in heart rate and arterial blood pressure. These data suggest that activation of PVN neurons leads to the release of ACTH, vasopressin, and oxytocin from the pituitary and a bradycardia that is mediated by the autonomic nervous system.

Darlington, Daniel N.↗

NASA NTRS1985

The Radioimmunoassay of Fluid and Electrolyte Hormones

The subject of the paper will be the assay of fluid/electrolyte hormones. ADH (antidiuretic hormone also referred to as vasopressin) reduces fluid loss by increasing water reabsorption by the kidney. The stimuli for its release from the pituitary are loss of blood, dehydration, or increased salt intake. Angiotensin II is the next hormone of interest. It is "generated" from a blood protein by the release of renin from the kidney. One of its functions is to stimulate the secretion of aldosterone from the adrenal gland. Release of renin is also stimulated by volume and sodium loss.

Keil, Lanny C.↗