Guillemette Gauquelin

Comparison of a 4-day confinement and head-down tilt on endocrine response and cardiovascular variability in humans

The aim of this study was to determine the effects of a 4-day head-down tilt (HDT; − 6°) and 4-day confinement on several indicators that might reflect a state of cardiovascular deconditioning on eight male subjects. Measurements were made of endocrine responses, heart rate variability and spontaneous baroreflex response (SBR) slope before, during and after each intervention. Plasma volume decreased by 10% after the 4-day HDT. The concentration of active renin was increased and that of urinary atrial natriuretic peptide decreased during the 4-day experiment in both groups. Plasma arginine vasopressin concentration decreased significantly only after 4-day confinement. After the 4-day HDT, one of the spectrum analysis parameters was statistically changed: the parasympathetic indicator decreased significantly (P < 0.05) whereas the sympathetic indicator and the total power spectrum were unaltered. After 4-day confinement spectrum analysis parameters were not statistically altered. A significant decrease of SBR (P < 0.05) was noticed only after the 4-day HDT. These data would suggest that exposure to a 4-day HDT was sufficient to induce a cardiovascular deconditioning which may have been induced by confinement and inactivity.

Radioimmunoassay of arginine vasopressin, oxytocin and arginine vasotocin-like material in the human pineal gland

Specific radioimmunoassays (RIAs) have been developed for arginine-vasopressin (AVP), oxytocin (OT), and arginine-vasotocin (AVT): they can detect 2.5 pg, 5 pg and 1 pg of hormone respectively. The three antisera employed in the RIAs in the present study all had a specificity that discriminated between the three neuropeptides and thus allowed their accurate measurement in each of 157 human pineal glands. Immunoreactive AVP was found to have a mean concentration of 306.4/+-27.6 (SE) pg/gland in the 1389 pineals where it was at level higher than the detection limit. Immunoreactive OT was determined as 386.3/+-42.1 pg/gland in the 110 pineals where it was measurable, and the mean apparent immunoreactive AVT content was 44.6/+-3.6 pg/gland in the 110 pineals where it was found at detectable levels. Cross-reactivity with AVP or OT cannot account for the immunoreactive peptide content of human adult pineal glands was demonstrated as a function of: (1) sex, (2) time of death, (3) cause of death, (4) age (18 to 85 yr old) or (5) delay between death and gland removal over the range of 4 to 48 hr. While the presence of AVP and OT is not surprising, indications of an immunoreactive AVT may in fact reflect a peptide which is closely related to AVT and cross-reacts in the AVT RIA.

A day/night rhythm of vasopressin and oxytocin in rat retina, pineal and harderian gland

Arginine vasopressin (AVP), oxytocin (OT) and neurophysins (Np) have been found in the pineal gland and the retina of the rat. Because the retina, pineal gland and Harderian gland (HG) serve analogous functions, we undertook a study to determine the presence of these peptides in these three organs of rats. They were detected by two specific methods: HPLC and specific radioimmunoassays. For Np, total neurophysins (NpT) were measured. To determine a 24 hr rhythm, the animals were maintained under a light/dark cycle of 12 hr/12 hr for 3 weeks. The pineal glands, retinae and HG were collected. Day/night rhythms of AVP, OT and NpT were demonstrated in the retina and HG; but the pineal gland had only AVP rhythm. A significant decrease in the rhythms at 4 a.m. was demonstrated in the retina and HG. The 24 hr variation of AVP in the retina seemed parallel to that of the HG.

Presence of vasopressin, oxytocin and neurophysin in the retina of mammals, effect of light and darkness, comparison with the neuropeptide content of the neurohypophysis and the pineal gland

Arginine vasopressin (AVP) and oxytocin (OT) as well as their CNS carrier neurophysins (Np) have been found in the pineal gland. In view of the analogy between the pineal gland and the retina, the contents of these neuropeptides in rat, human and bovine retinae were determined. AVP, OT and Np were detected by specific radioimmunoassay (RIA) and their presence confirmed by RIA measurements (1) in rat and human retinae on HPLC fractions and (2) by the detection of the C-terminal portion of the precursor to AVP and its associated Np = propressophysin (CPP). The AVP and OT content in the retina of the rat was modified by light: AVP and OT content was smaller at 2 a.m. than at 2 p.m., but was increased by a 7 day constant exposure to darkness. In contrast, pituitary content was decreased after 7 days of constant darkness. If one optic nerve was cut we observed a decrease in retinal AVP content compared to the contralateral side and a decrease in pituitary AVP content. Our data clearly demonstrated the presence of AVP, OT and Np in the retina and their variation induced by light. It is probable that these peptides are of central origin.

Atrial natriuretic factor: specific binding to renal glomeruli during the development of two-kidney, one clip hypertension in the rat

Blood pressure (BP), atrial and plasma concentrations of atrial natriuretic factor (ANF), hematocrit and renal glomerular ANF receptors were studied during the development of hypertension in two-kidney, one clip (2-K, 1C) rats and were compared with normotensive controls. Plasma ANF was elevated in the 2-K, 1C group in all stages of hypertension, even after 3 weeks when BP, although higher than in sham-operated animals, had not yet reached arbitrarily-set hypertensive levels. At this time, hematocrit was higher in the hypertensive rats than in the controls, but the difference later disappeared. Lower atrial ANF concentrations were observed in the 2-K, 1C group at week 3, but only in the right atrium. No difference in ANF levels was noted in either the left or right atrium between hypertensive and normotensive animals 5 and 7 weeks after clipping. The glomerular ANF receptor population was markedly smaller in the clipped left kidney of 2-K, 1C rats during all stages of hypertension, and in the untouched right kidney at 5 and 7 weeks after surgery, but was larger in the non-clipped right kidney in the pre-hypertensive phase (3 weeks). It is concluded that receptor density changes during the evolution of high BP in the 2-K, 1C Goldblatt model of experimental hypertension. Our data suggest that the increases and decreases in density of renal glomerular ANF receptors may play a role in the differential handling of sodium by the clipped and non-clipped kidney during the various stages of development of 2-K, 1C hypertension in the rat.

Cardiovascular effects of central injection of acetylcholine in anaesthetized dogs: a role for vasopressin release

1 The effect of an intracisternal injection of 20 μg kg−1 of acetylcholine was studied on systolic and diastolic blood pressures, heart rate, and plasma levels of noradrenaline, adrenaline, vasopressin, plasma renin activity and atrial natriuretic factor in chloralose‐anaesthetized dogs, 8 of which were normal and 7 with diabetes insipidus (deprived of vasopressin secretion by surgical lesion of the hypothalamoneurohypophysial system). 2 Acetylcholine significantly increased systolic and diastolic blood pressures in both groups of animals. However, the rise in blood pressure was significantly shorter lived in the dogs with diabetes insipidus. 3 Acetylcholine significantly increased plasma levels of noradrenaline but not adrenaline in control animals and in dogs with diabetes insipidus. Noradrenaline and adrenaline responses after acetylcholine were not different in the two groups of animals. 4 Acetylcholine induced a significant increase in vasopressin plasma levels only in control animals while in dogs with diabetes insipidus vasopressin remained at nearly undetectable levels. 5 Acetylcholine significantly increased atrial natiuretic factor plasma levels only in control dogs. 6 Although plasma renin activity increased in both groups of animals after the i.c. injection of acetylcholine, this change was not significant in any group. 7 These results suggest that, in the anaesthetized dog, the central injection of acetylcholine induces a rise in blood pressure through both an increase in sympathetic outflow and a release of vasopressin.

Characterization of renal glomerular endothelin receptors in the rat

Specific receptors for Endothelin (Et) have been identified in the glomerulus of rat kidney. Human 125I-ET binds to a single population of high affinity receptors in glomerular membranes from normal rats with a mean equilibrium dissociation constant of 200 pM. The binding was time and temperature-dependent, saturable and reversible. The Et-receptor complex was not affected by either vasopressin, atrial natriuretic factor or angiotension II.

Recording heart rate and blood pressure in rats during parabolic flight.

The way in which the cardiovascular system adapts to weightlessness is still under discussion. No data are yet available on the responses of rats during space flight, although this animal is commonly used in simulation studies. We have designed and tested a protocol to study the short term responses of the cardiovascular system to weightlessness during parabolic flight. A telemetry system was used to measure heart rate (HR) and blood pressure. It was possible to collect and record radio-signals without any interference. Microgravity caused a reduction in HR, an increase in mean arterial pressure (MAP, 7%), and a non-significant decrease in central venous pressure (CVP, 13%). The change in CVP was similar to the decrease observed in human space flight. This type of study may also be feasible for longer exposure of rats to microgravity (space flight).

Hormone changes induced by 37.5-h head-down tilt (−6°) in humans

Endocrine regulation of hormones and electrolytes during 37.5 h of −6° head down tilt (HDT) was studied in 13 men. The acute effects of simulated weightlessness are today well documented, but no study has been made concerning the hormone changes between 12 h and 2 days of HDT. Plasma volume showed a maximal increase of 9.23 (SEM 1.97) % after 6.5 h (P<0.01) and had returned to prestudy levels after 13.5 h of HDT. From 1.5 h to 4 h of HDT, C-terminus and N-terminus atrial natriuretic peptide (ANP) concentrations in plasma were increased by about 50% (P<0.01) and thereafter declined to pre-HDT levels. Plasma renin activity (PRA) was decreased by 47% (P<0.05) after 4 h of HDT; PRA increased after 23.5 h to 60%; noradrenaline concentration decreased immediately and remained low up to 37.5 h. Diuresis and natriuresis were evident during the 1st day of HDT, resulting in a marked increase in the urinary Na+. These results showed that the initial hormone (ANP, PRA) changes during HDT did not last more than 13.5 h and that after 24 h a new state would seem to have been established to adapt the body to hypovolaemia.

Central cardiovascular effects of acetylcholine in the conscious dog.

1 The effects of central cholinomimetic drugs on cardiovascular and vasoactive hormonal responses (blood pressure, heart rate, catecholamines, vasopressin, atrial natriuretic factor, neuropeptide Y plasma levels and plasma renin activity) were investigated in conscious Beagle dogs. For this purpose a catheter was chronically implanted into each dogs cisterna magna to allow repeated central injections in the awake animals. 2 Intracisternal acetylcholine (20 μg kg−1) significantly increased systolic and diastolic blood pressure. These changes were accompanied by an initial short term tachycardia followed by a long lasting bradycardia. Intracisternal acetylcholine also increased noradrenaline, adrenaline and vasopressin plasma levels, decreased plasma renin activity but did not modify plasma levels of neuropeptide Y and atrial natriuretic factor. 3 The effects of acetylcholine were completely abolished by pretreatment with intracisternal injection of the muscarinic antagonist, atropine (5 μg kg−1) but not by the intracisternal injection of the nicotinic antagonist, mecamylamine (25 μg kg−1). 4 The present results demonstrate that there are qualitative and quantitative differences between the central cardiovascular effects of acetylcholine in conscious dogs compared to what we previously reported, using a comparable protocol, in anaesthetized dogs. Under both conditions, we observed a central cholinergically mediated increase in blood pressure secondary to an increase in sympathetic tone and vasopressin release but these responses were shorter (less than 10 min) in the conscious dogs than in anaesthetized dogs (more than 10 min). Moreover, we detected in the response to the central cholinergic stimulation in the conscious dogs a significant increase in plasma adrenaline levels and biphasic changes in heart rate which were not described previously in the anaesthetized dog.