The Hypothalamo-Pituitary-Gonadal System: Role of Peptides and Sex Steroids

Abstract

The activity of the hypothalamo-pituitary unit is modified by a variety of modulatory influences either originating in the central nervous system or coming directly from the periphery. One type of input is represented by nervous signals which are transferred to the hypothalamic hormone producing neurons through the release, at neuronal junctions, of “classical” neuro-transmitters as well as of different classes of peptides. Although the available evidence cannot be reviewed in the present report, it has been clearly established that catecholamines, acetylcholine, serotonin, prostaglandins, histamine, gamma-aminobutyric acid, substance P, neurotensin, peptides common to the brain and to the gastrointestinal tract, opioid peptides are all involved in the regulation of the hypothalamo-pituitary function (see Müller et al., 1977; McCann, 1980; Morley, 1981, for references). It is interesting that some of the peptides present in the mammalian brain have also been identified in the amphibian skin (TRH, neurotensin, bombesin, etc.). Recently two new peptides, dermorphin and sauvagine, have been isolated from the skin of the South American frog, Phillomedusa sauvagei; they have been subsequently chemically identified and obtained by synthesis (Montecucchi et al., 1980; 1981). Evidence is accumulating which suggests that also these peptides may play a physiological role as modulators of the activity of the hypothalamo-pituitary unit (see Motta, 1985, for references). The other type of influence is hormonal in nature and is provided by the hormones produced in the peripheral target glands, by the pituitary hormones and possibly by the hypothalamic hormones themselves, which all act through different classes of feedback mechanisms in regulating the activity of the hypothalamo-pituitary system (see Piva et al., 1979, for references).