In vitro control of prolactin (PRL) and growth hormone secretion of neonatal rat pituitary glands: effects of ovine PRL, salmon calcitonin, endothelin-3, angiotensin II, bromocryptine and somatostatin

Development of fetal brain renin-angiotensin system and hypertension programmed in fetal origins

Since the concept of fetal origins of adult diseases was introduced in 1980s, the development of the renin-angiotensin system (RAS) in normal and abnormal patterns has attracted attention. Recent studies have shown the importance of the fetal RAS in both prenatal and postnatal development. This review focuses on the functional development of the fetal brain RAS, and ontogeny of local brain RAS components in utero. The central RAS plays an important role in the control of fetal cardiovascular responses, body fluid balance, and neuroendocrine regulation. Recent progress has been made in demonstrating that altered fetal RAS development as a consequence of environmental insults may impact on "programming" of hypertension later in life. Given that the central RAS is of equal importance to the peripheral RAS in cardiovascular regulation, studies on the fetal brain RAS development in normal and abnormal patterns could shed light on "programming" mechanisms of adult cardiovascular diseases in fetal origins.

Identification of the somatostatin receptor subtypes involved in regulation of growth hormone secretion in chickens

The effects of somatostatin (SRIF) are mediated through five distinct G-protein-coupled receptors (SSTR1-5). In the present study, pituitary cells from 6-week-old chickens were subjected to reverse hemolytic plaque assays for growth hormone (GH) in the presence of SSTR subtype specific nonpeptidyl agonists. A SSTR2 selective agonist (L-779,976) potently inhibited both basal and GH-releasing hormone (GHRH)-stimulated GH release at low nanomolar concentrations. A SSTR5 agonist (L-817,818) inhibited GH release only under basal conditions and in a subpopulation of somatotrophs. In contrast, a SSTR4 selective agonist (L-803,087) used at high nanomolar concentrations modestly stimulated GH release under basal conditions but did not influence GHRH-stimulated GH secretion. The SSTR1 and SSTR3 specific agonists did not affect GH secretion under any condition tested. Reverse transcription-polymerase chain reaction (RT-PCR) and Northern blot analysis using a partial cDNA for chicken SSTR2 showed relatively high levels of SSTR2 mRNA in the anterior pituitary (both in the caudal and cephalic lobes) and brain and detectable levels in liver, muscle, heart and small intestine. These results indicate that SSTR2 is the primary mediator of the inhibitory effects of SRIF on GH secretion in chickens.

Fatty acids and brain peptides

The role of fatty acids (FA) as a mediator and modulator of central nervous system activity in general, and peptides in particular, is only recently becoming understood. This paper reviews numerous findings concerned with the activity of fatty acids, particularly with their interaction with diverse neurochemical systems and their consequences for better understanding neurotransmitters, hormones and peptides. The effects include FA as precursors in the manufacture of neurochemical elements, including enzymes, neurotransmitters, and hormones. Of particular interest is the important changes in neuronal membrane composition that have been attributed to FA. Such changes may account for the changes in thermoregulation, learning, and other functions that accompany dietary manipulation of FA intake. While the total level of FA has been the object of many investigations, this report addresses the need to focus on the ratio of FA, especially alpha-linolenic/linoleic acid, which has been shown to be a critical factor in a number of research studies.

A sensitive assay for studying dopaminergic activity in cultures of rat pituitary cells

The dopaminergic and antidopaminergic activity of drugs is frequently assayed in pituitary cell cultures. Here we describe a modified version of the assay based on the use of pituitary cells from prepubertal female rats. Under our experimental conditions (50,000 cells well-1, 2-day culture and 2-h drug-exposure) the assay yielded high selectivity and sensitivity for drug dopaminergic activity. D2 agonistic activity of bromocriptine could be observed at a concentration as low as 10(-15) M, the antagonistic activity of haloperidol at 10(-16) M. The assay also proved reproducible and simple enough for routine screening of dopaminergic activity. The assay enabled dopaminergic agonist and antagonist activity to be revealed at very low drug concentrations. The high sensitivity of the assay could be of advantage in studying dopaminergic activity in samples containing active substances present at low concentrations or for disclosing the activity of substances with low dopaminergic potency.

Somatostatin receptor subtype specificity in human fetal pituitary cultures. Differential role of SSTR2 and SSTR5 for growth hormone, thyroid-stimulating hormone, and prolactin regulation

Somatostatin (SRIF), a hypothalamic inhibitor of pituitary growth hormone (GH) and thyroid-stimulating hormone (TSH) secretion, binds to five distinct receptor (SSTR) subtypes. We therefore tested SSTR subtype-specific SRIF analogs in primary human fetal pituitary cultures (23-25-wk gestation) to elucidate their role in regulating human pituitary function. Using reverse transcription-PCR, mRNA expression of SSTR2 and SSTR5 were detected in fetal pituitary by 25 wk. SRIF analog affinities were determined by membrane radioligand binding in cells stably expressing the human SSTR forms. GH secretion was suppressed equally (40-60%, P < 0.005) by analogs preferential for either SSTR2 (IC50 for receptor binding affinity, 0.19-0.42 nM) or SSTR5 (IC50, 0.37 nM), and compounds with enhanced affinity for SSTR2 were more potent (EC50 for GH suppression, 0.05-0.09 nM) than Lanreotide (EC50, 2.30 nM) and SRIF (EC50, 0.19 nM). Similarly, analogs with high affinity for SSTR2 or SSTR5 decreased TSH secretion (30-40%, P < 0.005). However, prolactin was effectively inhibited only by compounds preferentially bound to SSTR2 (20-30%, P < 0.05). Luteinizing hormone was modestly decreased (15-20%) by SSTR2- or SSTR5-specific analogs. An SSTR5-specific analog also exclusively inhibited GH in acromegalic tumor cells. Thus, SRIF regulation of GH and TSH in primary human fetal pituitary cells is mediated by both SSTR2 and SSTR5, both of which are abundantly expressed by 25 wk. In contrast, suppression of prolactin is mediated mainly by SSTR2. These results indicate that SSTR5 is critical for physiologic regulation of GH and TSH. SRIF analogs with selective affinity for this receptor may therefore be more effective in the treatment of hormone-secreting pituitary adenomas.