Action Of Hypothalamic Hormones Research Articles

Action of hypothalamic hormone on nude mice with transplantable strains of human tumors

Action of hypothalamic hormone on nude mice with transplantable strains of human tumors

Mechanism of Action of Hypothalamic Hormones in the Adenohypophysis

The observation of a close parallelism between changes of cyclic adenosine 35 monophosphate (cAMP) accumulation and specific hormone release under the influence of 2 stimulatory hypothalamic hormones thyrotropin-releasing hormone (TRH) and luteinizing hormone-releasing hormone (LHRH) and 1 inhibitory peptide (somatostatin) strongly suggest that the adenylate cyclase system is involved in the mechanism of action of these 3 peptides in the anterior pituitary gland. The mechanism (depicted in a figure) is supported by data obtained on the characteristics of the TRH receptor and properties of adenohypophyseal cAMP-dependent protein kinase and its substrates. Estrogen treatment in vivo led to an increase in the number of adenohpophyseal TRH receptors whereas opposite effects were seen after thyroid hormone administration. In vitro pituitary cell primary cultures showed that estrogens stimualted both LH and follicle stimulating (FSH) hormone secretions while androgens had opposite effects on the secretion of the 2 hormones markedly inhibiting LH and stimulating FSH. The effect of progesterone in estradiol-primed cells was biphasic LH secretion whereas the effect on FSH secretion was exclusively stimulatory. Inhibin activity of ovarian and testicular origin was a potent inhibitor of basal FSH release. Recent data indicate that dopamine may be the main or even the only inhibitory substance of hypothalamic origin controlling prolactin secretion. Estrogens were found to stimulate the prolactin secretion directly at the pituitary level and to reverse the inhibitory effect of dopamine agonists on prolactin secretion.

In vivo methods for studying the action of hypothalamic hormones with special reference to their antisera as tools for investigation.

Physiological actions of the hypothalamic hypophysiotropic hormones were extensively studied before these hormones were isolated. Experiments were performed using crude extracts of hypothalamic tissue in order to understand the action of a hypothalamic hormone. The physiological role of a hypothalamic hormone was indirectly studied by suppressing or stimulating production or release of the hormone by making a lesion or stimulating a certain area in the brain. To learn its biokinetics, the content of the hypothalamic hormone under various conditions was measured by using bioassays. The e-normous amount of data thus accumulated by many investigators has greatly contributed to our knowledge of neuroendocrinology.

Peptidase inactivation of hypothalamic releasing hormones.

With the structural characterization of the hypothalamic hormones, luteinizing hormone-releasing hormone (LH-RH), thyrotrophin-releasing (TRH), melanocyte-stimulating hormone release-inhibiting hormine (MIH), and growth hormone release-inhibiting hormone, (GH-RIH or somatostatin), it has been possible to investigate their enzymic inactivation by peptidases which are present at various sites in the body. Enzymes may play an important part in the control of polypeptide hormone levels and the peptidases acting on these four hypothalamic hormones may regulate the amount of TRH, LH-RH, MIH and somatostatin released from the hypothalamus, or their action at the level of the pituitary and their removal from the circulation. By studying the peptidase enzymes, further information may be obtained on the physiological mechanisms controlling the secretion and actions of hypothalamic hormones, as well as on the design of analogues with increased or competitive activity.