RELATIONSHIP BETWEEN HYPOPHYSEAL PORTAL GHRH AND SOMATOSTATIN AND PERIPHERAL GH LEVELS IN THE CONSCIOUS SHEEP

The mechanisms involved in the genesis of pulsatile GH secretion are n ot well understood. Recently, methods for hypophyseal portal blood col lection in conscious sheep became available. Using this method, GHRH a nd SRIH secretion into hypophyseal portal blood (HPB) and GH release f rom the pituitary gland were simultaneous assessed and the relationshi p between GHRH and SRIH changes in HPB and GH in peripheral blood was investigated. In 23 rams (9-11 month old, 35-45 kg bw), 126 hours of H PB were analysed. Fifty-four spontaneous GH peaks were detected. The m ajority of GH peaks (48.1%) was associated with an increased portal GH RH and a fall in somatostatin concentrations. A simultaneous increase in GHRH and somatostatin levels was observed in 18.5% of GH peaks whil e 12.9% of peaks occurred with a fall in SRIH and no modification in G HRH concentrations. Finally, 5/54 (9.3%) GH peaks occurred without any modification in portal GHRH and SRIH release. Our data indicate that the GHRH/SRIH interplay is complex. The occurrence of spontaneous GH p eaks may be due not only to a coordinate increase in GHRH and reductio n in SRIH release similar to male rat, but also to other patterns of G HRH/SRIH secretion.