Seasonal variations in vasopressin secretion in rats

Effect of surgical deafferentation of the hypothalamic supraoptic nucleus on urinary vasopressin levels in twenty-month-old rats

Indices of water balance (daily water consumption, urine volume, and urine osmolality), and vasopressin (VP) urinary excretion were measured in 3-month-old (m.o.) and 20 m.o. F344 rats after neurosurgical lesion of noradrenergic afferents to the supraoptic nucleus (SON) in the medial forebrain bundle (mfb), in order to assess whether morphological denervation (21) was functionally effective. Lesion of the mfb was accomplished using a mechanical knife cut placed stereotaxically medial and caudal to SON. The experiment was performed three times. Morphological evaluation consistently indicated a marked depletion of noradrenergic afferents in SON after lesion placement. The effect of the lesion on daily excreted VP was assessed by paired t-test, using means of equal numbers of urinary VP measurements representing 13-15 days each pre- and postsurgically for each animal. The postsurgical interval for assessing the functional effect of the lesion was chosen based upon morphological evidence for mfb regeneration at 14 days (21). Three m.o. rats showed comparable urinary VP levels before (mean = 328.4 +/- 97.3 pg/24 hr/100 g b.wt., for 10 rats for 2 weeks) and after (354.7 +/- 63.0 pg/24 hr/100 g b.wt.) lesion placement. In 20 m.o. rats, overall mean postsurgical VP excretion was 199.4 +/- 44.8 pg for 15 rats for 2 weeks, compared with a presurgical mean of 343.2 +/- 86.2 pg/24 hr/100 g b.wt. Mean urine VP was lower in 20 m.o. rats in each of three experiments; VP levels after lesion in 3 m.o. rats was lower in 2, but higher in one experiment; mean differences were not statistically significant for treatment (lesion) effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related differences in the incorporation of 3H-arginine into vasopressin in Fischer 344 rats

We studied the effect of aging on the incorporation of 3H-arginine into vasopressin (VP) molecule in the hypothalamus (HT) and the rate of its transport into the neurohypophysis (NH) of male Fischer 344 rats of different ages: 2-3 months (young, n = 28), 11-13 months (adult, n = 30) and 30 months (old, n = 27). 3H-arginine was injected in a single dose through a permanent cannula into the lateral ventricle of an awake animal. The rats were decapitated 1, 6, and 24 h after the injection. VP was extracted from individual HTs and NHs (without pars intermedia), purified in a chromatography column and determined by RIA. Hypothalamus: One hour after the injection the 3H-activity was highest in the young, lower in the adult and lowest in the old rats, whereas the specific activity (cpm/pg VP) was similar in all age groups, reflecting endogenous VP content to be highest in the young, lower in the adult and lowest in the old rats. In the young rats both activities decreased 6 and 24 h after the injection. The adult rats also exhibited declining activities, whereas in the old rats the activities remained unchanged from 1 to 24 h after the injection. Neurohypophysis: One hour after the injection of radioactive label 3H-activity and specific activity were significantly lower in the NH of the old than in those of young and adult rats. The activities increased 6 h after the injection in all age groups with the lowest values in the old rats. After 6 h, both activities in the old rats reached only the 1-h values of the young and adult rats suggesting a delay of at least 6 h in the axonal transport of newly synthetized VP in aged rats. Twenty-four hours after the injection both activities increased in all age groups exhibiting no difference among the age groups, indicating a decreased release of the newly synthetized VP from the NH of aged rats. These data demonstrate an age-related decrease in the rate of incorporation of 3H-arginine into VP, in the rate of its axonal transport and in the release of newly synthetized VP from the NH of Fischer 344 rats.

Seasonal variations of human lumbar CSF neurotransmitter metabolite concentrations

While circadian rhythms of many biological processes have been well characterized in humans, variations throughout the year have been little studied. Lumbar cerebrospinal fluid (CSF) neurotransmitter metabolite levels for homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenyl glycol (MHPG) were determined in patients with schizophrenia and Alzheimer's disease. Samples from both groups taken during October through March had significantly higher levels of HVA and 5-HIAA, but not MHPG, than samples from April through September.

Vasopressin and oxytocin content in cerebrospinal fluid and in various brain areas after administration of histamine and pentylenetetrazol

The content of vasopressin (AVP) and oxytocin (OXT) in the septum, hippocampus, hypothalamus and cortex was determined at 5 min and 24 hr after peripheral (intraperitoneal) administration of histamine (20.0 mg/kg) and pentylenetetrazol (45.0 mg/kg) and in the cerebrospinal fluid at 24 hr after pentylenetetrazol treatment. At 5 min after administration of histamine the AVP content in the septum was increased whereas the OXT level in the various areas was not changed. At 24 hr, neurohypophyseal peptide contents were unaffected in the brain regions analyzed. Pentylenetetrazol did not alter AVP content at 5 min after its administration, however, the OXT level in the septum and the cortex was diminished. At 24 hr after administration of pentylenetetrazol a decreased AVP content in the hippocampus and in the cortex was observed. In contrast, OXT content in the cortex was increased at this time. AVP and OXT levels in CSF were not changed at 24 hr following pentylenetetrazol treatment. The present results suggest that the levels of neurohypophyseal hormones can be differentially altered in particular brain regions at short- (5 min) and long- (24 hr) term intervals after treatment with histamine or pentylenetetrazol. Long-term changes in AVP and OXT levels after pentylenetetrazol may be implicated in the amnesic properties of this convulsive drug. Furthermore, the present findings point to a possible relationship with previously reported pentylenetetrazol-induced changes in peptide levels in the CSF.

The effect of microwave irradiation on vasopressin in plasma and hypothalamo-neurohypophyseal system

Radioimmunoreactive vasopressin was measured in plasma, neurohypophysis and hypothalamus of the rats after different procedures of killing: a) microwave irradiation; b) decapitation; c) decapitation following a stress induced by immobilization in a restrainer. Vasopressin content in the neurohypophysis and hypothalamus was much lower in microwave irradiated than in both decapitated and stressed decapitated rats. In addition, the data from microwave technique were inconsistent with a large scatter. Plasma vasopressin concentration was elevated in both the microwave irradiated and stressed decapitated rats, demonstrating that restraining of the animals induced an excessive stress. Microwave irradiation technique including the necessary manipulation of the animal proved to be less suitable than decapitation technique for the measurement of vasopressin. It is likely that vasopressin in the hypothalamus and neurohypophysis is relatively resistant against post-mortem proteolysis.

The effect of aging on vasopressin system in Fisher 344 rats

Vasopressin (VP) was measured by RIA in the plasma, neurohypophysis (NH) and hypothalamus (HT) of young (2 months), adult (12 months) and old (30 months) male Fisher 344 rats, ten of each age. Plasma VP concentration was significantly lower in old compared to adult and to young rats. VP content in the NH expressed per mg weight was similar in all three groups, while the hypothalamic VP content was decreased in the aged rats. This suggests that reduced synthesis and release and/or increased degradation of VP occurs in aged rats. These data are in an agreement with our previous results obtained with Sprague-Dawley rats indicating that these differences are not strain-related. In a pilot experiment, we further studied VP release from isolated perifused NH of young and old rats. Two glands of each age were simultaneously perifused in individual microchambers with medium TC 199 and subsequently stimulated by Locke's medium containing 56 mM K+. Both, the initial and the basal VP release from the NH of the old rats, as well as the response to high K+, were about a half that of the young rats. Thus, a decreased VP release may contribute to the findings of lower plasma VP concentration in aged rats.

Effects of constant bright illumination on reproductive processes in the female rat

Physiological and behavioral reproductive changes in the female rat which occur under constant bright illumination (LL) are examined. The development of LL-induced persistent estrus (PE) is discussed first in relation to other conditions in which PE is displayed. Next, mechanisms are reviewed which may account for the LL-induced changes. These include: (1) role of the retina, the retinohypothalamic tract and the suprachiasmatic nucleus; (2) influence of adrenal, pineal and Harderian glands; and (3) disruptions in either the 4-day endocrine rhythms or circadian neural component of the estrous cycle. Additional topics which are examined include the ontogeny of age-induced PE and the effects of LL on hormone receptor binding, puberty, sexual receptivity and mating.

Age-related vasopressin changes in rat plasma and the hypothalamo-hypophyseal system

Immunoreactive vasopressin (VP) weas measured in the plasma, neurohypophysis (NH) and hypothalamus (HT) of young (3 months), adult (12 months), and old (30 months) Sprague-Dawley male rats, both intact and anesthetized with halothane. VP content in the HT of the old rats was about half that of young and adult rats. Total VP content in the NH increased with age, reflecting large glandular size in the old rats. However, VP content was similar in all three groups, when expressed per mg of wet tissue. Plasma VP concentration was undetectable in the old intact rats and it rose to the levels of intact young or adult rats during halothane anesthesia. The anesthesia-related increase in plasma VP concentration was statistically significant in young but not in adult rats. These results suggest that in the intact rats during aging: (1) the synthesis of VP in the HT may be reduced; (2) the storage of VP in the NH is not impaired; and (3) the undetectable plasma VP concentration may reflect either reduced VP release or increased degradation.

Vasopressin release by histamine in the conscious goat

The vasopressin releasing activity of histamine was studied in conscious goats. Histamine was infused into the brain ventricles or intravenously and serial blood samples were taken from the jugular vein. Plasma vasopressin was assayed by a radioimmunoassay for arginine vasopressin (AVP). After i.v. infusions of 300 micrograms and 1 mg of histamine, a pronounced increase in plasma AVP up to greater than 100 pg/ml occurred. This was considered secondary to hypotension, since it only occurred with doses that markedly decreased arterial blood pressure. When given i.c.v. even smaller doses of histamine increased plasma AVP without any concomitant decrease in blood pressure. There was a simultaneous decrease in renal free water clearance in hydrated animals. Up to the dose of 300 microgramshistamine, the increase in AVP was modest. Histamine 1 mg i.c.v., given to either hydrated or non-hydrated animals, increased plasma AVP about tenfold, up to 38.3 +/- 23.3 pg/ml and 56.7 +/- 19.0 pg/ml, respectively. In individual experiments the correlation between the AVP level and the degree of antidiuresis was less apparent, since the kidney seemed to be very sensitive even to small changes in plasma AVP. It is concluded that histamine releases vasopressin through a central mechanism and it is reasonable to suppose that histamine may act as a neurotransmitter in the vasopressin releasing system.