Somatostatin at Low Doses Stimulates Growth Hormone Release from Intact Cultures of Porcine Pituitary Cells

Somatostatin (SRIF) is the primary inhibitory factor in the control of growth hormone (GH) release from somatotropes. This concept emerged from studies based mainly on the rat and human model. However, recent data suggest that the role of SRIF in the regulation of pituitary CH release might be different in other species such as the pig. Thus, in previous studies, we have demonstrated a dual (stimulatory/inhibitory) effect of SRIF on GH secretion in vitro in two porcine somatotrope sub-populations. In the present study, we have investigated whether SRIF can act as a GH-releasing factor in intact cultures of porcine somatotropes. To this end, both dose-related effects of SRIF on basal GH release and its effects on GH-releasing factor (GRF-)stimulated GH secretion were evaluated in monolayer cultures of porcine pituitary cells. SRIF did not affect basal secretion at the highest doses tested (10^-5, 10^-7, and 10^-9 M), whereas it induced a significant increase in GH secretion when applied at low doses (10^-11, 10^-13, and 10^-15 M). High-dose (10^-7 M) SRIF significantly reduced GRF-induced GH secretion, an effect that was absent at the lowest dose (10^-15 M) of the peptide tested. These results confirm the dual role af SRIF on GH secretion from porcine somatotropes, and demonstrate that SRIF, at low doses, can act as a true GH-releasing factor.

Key words

Somatotrope (Pig) - GH Secretion - SRIF (Stimulatory Effect) - GRF - Paradoxical Response