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Biomedical subjects

J Meites

Publications and source records attributed to J Meites.

At least 127 records · Page 7Linked to original sources
PubMed1978

Activity alterations of metabolic enzymes in the anterior pituitary of female rats during acute and chronic starvation, as well as after refeeding.

The activity of glycolysis and hexose monophosphate shunt decreases while the activity of some oxydative enzymes and acid phosphatase increases in the anterior pituitary of adult female rats during starvation. The alterations depend on the severity of starvation. The polypeptide hormone production also decreases. A close relationship exists between the metabolic activity of the gland and its endocrine function.

Acid Phosphatase↗
PubMed1978

Relation of biogenic amines to onset of puberty in the female rat.

Changes in hypothalamic concentration and turnover index (TI) of norepinephrine (NE), dopamine (DA), and serotonin (5HT) were studied during the first estrous cycle at the onset of puberty. Rats were killed when 40% of the population showed open vaginas. They were classified according to the state of their reproductive tract and serum LH values, as in anestrus, early proestrus, late proestrus, estrus, or diestrus. Serum LH, PRL, and hypothalamic LHRH were measured by RIA. The TIs for DA and NE were measured by estimating their rate of decrease after administration of alpha-methyl-para-tyrosine, and for 5HT-TI by its increase after pargyline administration. An increase in NE-TI in the hypothalamus was observed between anestrus and early proestrus, a decrease in DA-TI during early and late proestrus, and a small increase in 5HT-TI between early and late proestrus. LH and PRL peaks were observed at late proestrus when DA-TI and NE-TI reached their lowest values and hypothalamic LHRH concentration was failing. After late proestrus, the DA-TI rose sharply, NE-TI remained essentially unchanged. 5HT-TI fell, and serum LH and PRL declined to basal levels. These results suggest that the LH and PRL surges at late proestrus during the first estrous cycle at puberty are associated with an increase in NE-TI at early proestrus, a progressive decline in DA-TI at early and late proestrus, and an increase in 5HT-TI at late proestrus.

Animals↗
PubMed1978

Patterns of sex steroid and gonadotropin secretion in aging female rats.

Serum estradiol, progesterone, LH, and FSH were determined by RIA in 20- to 30-month-old constant estrous (CE), irregular pseudopregnant (PP), and anestrous (AS) female rats and from 4- to 5-month-old cycling female rats. Disruption of the estrous cycle in aging rats was associated with major changes in secretion of pituitary gonadotropins and ovarian steroids. None of the old rats, in contrast to the young rats, showed cyclic changes in any of the hormones studied. Serum progesterone was much higher in the PP than in the other two old groups, serum estradiol averaged somewhat higher in the CE than in the other two aged groups, and all four hormones were lower in the AS rats than in any other group. Basal serum FSH values were higher in the old CE rats than in either of the other old age groups and were slightly higher than in young rats on the afternoon of proestrus or morning of estrus. Serum FSH values were lower in the old PP and AS rats than in young rats on the afternoon of proestrus or morning of estrus. Serum FSH values were lower in the old PP and AS rats than in young rats on the afternoon of proestrus or morning of estrus. Serum values in the old CE rats were about the same as in young rats on the morning of proestrus or estrus, about the same in old PP rats as in young rats during diestrus, and were undectable in old AS rats. Since the ovaries of old rats are capable of near normal function under appropriate gonadotropic stimulation, it is concluded that the major cause for cessation of regular estrous cycles in old rats lies in altered hypothalamo-pituitary function.

Aging↗
PubMed1977

Evaluation of research on control of prolactin secretion.

At least three substances have been reported to be present in the hypothalamus that can inhibit prolactin release, namely a PIF, catecholamines and acetylcholine. At least four substances have been reported to be present in the hypothalamus that can stimulate prolactin release, namely PRF, TRH, serotonin and prostaglandins. Neither the existence of a distinctive PIF or PRF in the hypothalamus can be considered as definitely established. The predominant action of the mammalian hypothalamus on prolactin release is inhibitory under most conditions, and is stimulatory in avian species. In addition to control by the hypothalamus, several hormones and drugs can act directly on the pituitary to alter prolactin release. The interrelationships of these agents within and without the hypothalamus on prolactin secretion are complex, and there are many questions about their mode of action. Studies on the regulation of prolactin secretion have resulted in development of many methods for either increasing or decreasing release of this important hormone, and thereby have provided opportunities for influencing lactation, growth of mammary and pituitary tumors and other tissues responsive to prolactin.

Animals↗
PubMed1977

Effect of aging on hypothalamic LH-releasing and prolactin inhibiting activities and pituitary responsiveness to LHRH in the male laboratory rat.

Hypothalamic content of LH releasing and prolactin inhibiting activities and pituitary responsiveness to LH releasing hormone was measured in young (4 mo.) and aged (26 mo.) Long-Evans rats by in vitro methods. Hypothalamic extracts (0.5 and 1.0 hypothalamic equivalents) from young and aged male rats were incubated with untreated hemisected rat pituitaries in medium 199. Doses of 0.5 and 1.0 hypothalamic equivalents (HE) from both age group stimulated LH secretion. The increase in pituitary LH release stimulated by 0.5 HE from aged male rats was about half that stimulated by 0.5 HE from the young male group (p less than .20). The increase in LH secretion stimulated by hypothalamic extracts of either age group was not associated with a change in pituitary LH content. Although 0.5 and 1.0 HE from young male rats and 1.0 HE from the aged group reduced incubated pituitary prolactin release, 0.5 HE from the aged males did not affect prolactin release. Treatment with hypothalamic extracts also resulted in increased pituitary prolactin concentrations. Pituitaries from young and aged male rats were incubated in medium 199 containing 0, 25, or 100 ng of LH releasing hormone. Although LH releasing hormone stimulated LH secretion in all groups, the increase in release of LH was less in the aged groups than from pituitaries from the young male rats. Pituitary LH content of the aged male group was only about 1/4 that of the young group.

Aging↗
PubMed1977

Neuroendocrine control of prolactin in experimental animals.

Hypothalamic regulation of prolactin secretion in animals (mammals) and man appears to be similar, and no significant differences have yet been demonstrated. The hypothalamus contains neurotransmitters and polypeptides that can either inhibit or stimulate prolactin release, although the predominant influence under basal conditions is to inhibit prolactin release. Thus pituitary stalk section or placement of lesions in the basal tuberal region of the hypothalamus results in increased prolactin release and sometimes in initiation of lactation. Among agents in the hypothalamus that can inhibit prolactin release, the most important appear to be an as yet unidentified polypeptide prolactin release inhibiting factor (PIF) and dopamine. There is some evidence that dopamine may account for most, if not all, of the prolactin release inhibiting activity of the hypothalamus. Agents that increase dopamine activity, i.e. L-dopa, monoamine oxidase inhibitors, etc., depress prolactin release. Acetylcholine also can inhibit prolactin release, but it appears to act via the catecholamines. Of the agents in the hypothalamus that stimulate prolactin release, the most important appear to be an as yet uncharacterized polypeptide prolactin releasing factor (PRF), thyrotropin releasing hormone (TRH) and serotonin. TRH is as effective in releasing prolactin as in releasing TSH, but under most physiological states, TSH and prolactin release do not occur together. Serotonin and its precursors, tryptophan and 5-hydroxytryptophan, are powerful releasors of prolactin and have been shown to be involved in some physiological states in which prolactin is released, i.e. during suckling, stress, etc. Other agents in the hypothalamus that can stimulate prolactin release include GABA and some prostaglandins, but these have not yet been shown to be involved in physiological control of prolactin secretion. Exteroceptive stimuli that alter prolactin release act through the CNS and hypothalamus, but some hormones and drugs also can act directly on the pituitary to promote or depress prolactin release.

Acetylcholine↗
PubMed1977

Inhibition by prolactin of post-castration rise in LH.

Castration of male and female rats resulted in a marked rise in serum LH. The rise in serum LH was partially or completely prevented by injection of prolactin (Prl), by implantation of a small amount of Prl in the median eminence (ME), by grafting 2 anterior pituitaries (APs) underneath the kidney capsule, or by transplantation of a Prl-secreting pituitary tumor underneath the skin. The larger pituitary tumor transplants secreted more Prl and were more effective in reducing LH release than the smaller tumors which secreted less Prl. Suppression of LH release generally was greater during the earlier than in the later phases of the different treatments. The pituitary LH response to synthetic LH-RH was the same in ovariectomized rats with or without pituitary grafts, and the decrease in hypothalamic LH-RH after orchidectomy was prevented by pituitary grafts. These results indicate that Prl can depress LH release after castration and that these effects are mediated via the hypothalamus.

Animals↗
PubMed1977

Relation of gonadotropin secretion by pituitary grafts to spermatogenesis in hypophysectomized rats.

In hypophysectomized male rats, 2 anterior pituitary (AP) grafts placed underneath the kidney capsule partially prevented atrophy of the testes and ventral prostate during a 17 day post-implantation period. Spermatogenesis was partially maintained as revealed by histological examination of the testes. The AP grafts released small amounts of LH and FSH and substantial amounts of prolactin as determined by radioimmunoassay. Serum LH and FSH were undetectable in the hypophysectomized rats with no AP grafts. Inhibition of prolactin release by daily injections of ergocornine methanesulfonate (ERG) did not significantly alter serum levels of FSH and LH, spermatogenesis or testes and ventral prostate weights, indicating that circulating levels of prolactin were not responsible for the partial maintenance of spermatogenesis and prostate weight in these rats. Daily injections of ovine prolactin also had no effect on spermatogenesis or prolactin also had no effect on spermatogenesis or prostate weight in the hypophysectomized rats, and there was no change in the histological appearance of the testes and prostate. These observations indicate that secretion of gonadotropins and not prolactin by AP grafts accounts for the partial maintenance of spermatogenesis and prostate weight in hypophysectomized, AP-grafted male rats during the experimental period studied.

Animals↗