Hypothalamic Fragments Research Articles

Pituitary portal vessel infusion of hypothalamic extract and release of LH, FSH and prolactin.

Extracts of hypothalamic tissue (HE) or of cerebrocortical tissue were infused into stalk portal vessels of anesthetized male rats. The extract of cerebrocortical tissue, equal in weight to ½ of a hypothalamic fragment, had no effect on the release of LH, FSH, or prolactin. HE caused an increase in the levels of LH and FSH in arterial plasma and simultaneously a decrease in the level of prolactin. The responses to HE were related to the concentration of the extract. For example, in rats given HE equivalent to ½1 ⅙, or ½ of a hypothalamic fragment per 30 min, the concentrations of LH in plasma at the end of the infusion period were 2.5, 4.5 and 6.9 times the control values, respectively. The corresponding levels of FSH were 1.6, 2.2 and 2.9, and of prolactin 0.73, 0.55 and 0.37. After the infusion of HE was terminated, the concentrations of LH and FSH in plasma fell and that of prolactin rose. The half-times of the disappearance functions of prolactin, LH and FSH in plasma of rats after hypophysectomy were...

Further Studies of Stimulation of Anterior Pituitary Cyclic Adenosine 3',5'-Monophosphate Formation by Hypothalamic Extract and Prostaglandins

Abstract Crude ovine hypothalamic extract in vitro increased the formation of cyclic adenosine 3',5'-monophosphate (cyclic AMP) by rat anterior pituitary glands but not by posterior pituitary, pineal, adrenal, or liver. Epinephrine (30 µg per ml) stimulated formation of cyclic AMP in pineal gland and adrenocorticotropic hormone- (8 i.u. per ml) and glucagon-(100 µg per ml) augmented cyclic AMP in adrenal and liver, respectively. Hypothalamic extract also rapidly increased adenyl cyclase activity in homogenates of rat anterior pituitary glands. Although theophylline (10-2 m) inhibited phosphodiesterase activity in anterior pituitary homogenates, hypothalamic extract had no effect on this enzyme either in the presence or absence of theophylline. Theophylline addition increased the concentration of anterior pituitary cyclic AMP and potentiated effects of hypothalamic extract on this parameter, but had no effects on luteinizing hormone release. Hypothalamic extract did not inhibit ATPase activity. Exclusion of Ca2+ from the buffer did not diminish stimulation of cyclic AMP formation by hypothalamic extract. Anterior pituitary cyclic AMP was not increased by high K+ concentration in the incubation medium. Prostaglandins added in vitro also increased formation of cyclic AMP by anterior pituitary, but there was marked variation in their potency. Prostaglandin E1 was the most effective and F1α the least. However, none of the prostaglandins increased luteinizing hormone release in vitro. Hypothalamic extract and prostaglandin E1 stimulated 3H-adenine incorporation into 3H-labeled cyclic AMP in intact anterior pituitary glands. NaF did not increase 3H-adenine incorporation into 3H-labeled cyclic AMP in intact pituitary in vitro, although it markedly increased adenyl cyclase activity in pituitary homogenates. Epinephrine (200 µg per ml) did not modify the stimulation by hypothalamic extract of either cyclic AMP synthesis or luteinizing hormone release. Carbamylcholine (30 µg per ml), dopamine (30 µg per ml), serotonin (30 µg per ml), prostaglandin E1 (10 µg per ml), or histamine (30 µg per ml) added in vitro had no effect on cyclic AMP concentrations in hypothalamic fragments.

A study of ACTH and CRF in chickens

Previous work had demonstrated that chicken pituitaries contained a substance which was able to cause corticosterone synthesis by adrenals in vitro. In the present study chicken pituitary glands were assayed by the adrenal ascorbic acid-depletion method in hypophysectomized rats. It was found that perfect parallelism existed between the doses of 1.5–96.0 μg/100g body weight of chicken adenohypophyses and 0.4–10.0 mU of a standard mammalian ACTH. The data presented show that chicken pituitary glands contain relatively more ACTH than do those of rats. When assayed on hypophysectomized rats, perfect parallelism was demonstrated between extracts of 10, 20, and 40 chicken hypothalamic fragments and 0.4, 2.0, and 10.0 mU of the ACTH standard. Similar data were obtained on intact blocked rats. These results led to the conclusion that chicken hypothalami contain ACTH or an ACTH-like substance. No activity was present in extracts of chicken cerebral cortices which were used as control test substances.

Elevation of thyrotropin release by intrapituitary infusion of crude hypothalamic extracts.

In rats whose endogenous pituitary secretion had been depressed by phenobarbital and raised ambient temperature (34 C), increases of 131I levels in blood were measured following intrapituitary infusion (4.5–7 μl/hr for 2.5–3 hr) of extracts prepared from the hypothalami of rats and sheep. It was shown that the intrapituitary infusion technique was a sensitive method for testing thyrotropin-releasing factor (TRF) activity provided precautions were taken to prevent cytolysis due to faulty pH or tonicity of the solutions infused. Intrapituitary infusion of dialyzed extracts of rat hypothalamus and of stalk-median eminence (SME) and hypothalamic fragments from sheep at different dosages showed that the magnitude of the response increased with increasing dosage. Intrapituitary infusions of saline or intravenous infusions of sheep hypothalamic extract did not increase blood 131I levels, indicating that neither pituitary damage due to infusion nor TSH contamination of the extracts was responsible for the results. In the sheep, the concentration of TRF in the SME was approximately twice that in the hypothalamus but the latter contained 7 times as much TRF. When compared with 131I responses obtained from intravenous infusion of TSH at 3 dose levels, it was estimated that intrapituitary infusions of TRF in this experiment released only about 5 % of the TSH present in the pituitary store. (Endocrinology81: 113,1967)

INFLUENCE OF HYPOTHALAMIC FRAGMENTS AND EXTRACTS ON LACTOGEN PRODUCTION IN VITRO.

Anterior pituitaries from estrous cyclic and lactating, hooded Norway rats were cultured in synthetic medium (Mixture 199) with hypothalamic extracts or frag ments for a period of 3 days at a 300 cc/min gas flow of 95% Oz-5% COe. In 5 experiments, lactogen production was decreased an average 22.3% by the addition of hypothala mus. Hypothalamic extracts and hypothalam ic fragments from either estrous cyclic or lactating animals were capable of inhibiting pituitary lactogen production in vitro. Addition of cerebral cortical extracts to the culture system did not significantly alter lactogen production. Lactogen content of cultured pituitary tissue and AP viability ratings of hypothalamic groups did not differ significantly from those of controls.