The release of biologically and immunologically reactive somatostatin from perifused hypothalamic fragments

The purpose of this investigation was to 1) develop a hypothalamic perifusion system which would allow measurement of spontaneous basal somatostatin (SRIF) release, 2) compare the immunological and biological activities of released SRIF, and 3) study the effect of membrane depolarization, extracellular calcium, and several neurotransmitters on SRIF release. Release was greater at the beginning of the perifusion and decayed with time for 90 min, after which it stabilized and remained constant for 3 h, the period used to determine the mean rates of release. Basal release was 20.2 pg/fragment x 10 min. Membrane depolarization with 55 mK K+ increased SRIF release 30 to 4-fold in a calcium-dependent manner. The immunoreactivity and biological activity of SRIF concentrated by affinity chromatography of hypothalamic perifusates were compared to those of synthetic SRIF and rat hypothalamic extract. Biological activity was assessed by the inhibition of radioimmunoassayable rat GH released from cultured dispersed rat anterior pituitary cells. Hypothalamic fragments were exposed to several neurotransmitters as well as other substances known to influence rat GH secretion. Our results may be summarized as follows. 1) The perifused medial basal hypothalamus releases immunoactive and bioactive SRIF at a constant basal rate. 2) Membrane depolarization with high potassium stimulates a small releasable pool of SRIF in a calcium-dependent manner. 3) Affinity chromatography is an alternative technique to collect and concentrate SRIF released from tissues. 4) Common neurotransmitter agents did not modify SRIF release from the medial basal hypothalami under the present conditions.