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We have studied the effects of vasoactive intestinal peptide (VIP) on PRL secretion in a Bio-Gel column parafusion system containing rat pituitary tumour cells (GH4C1). A dose-dependent increase in PRL release was observed with half-maximal and maximal effect (2.1-fold) at 8 X 10(-8) and 5 X 10(-6) M, respectively. The PRL-stimulatory effect of VIP was instantaneous and maintained during the parafusion experiments (up to 60 min). On a molar basis VIP was always less effective than thyroliberin (THR), and the maximum stimulation of PRL release obtained with TRH was 1.2-3.0-fold higher (n = 12) than the maximum effect seen after VIP administration. The PRL-releasing effects of VIP, THR and high extracellular K+ were almost completely abolished in the presence of two inhibitors of voltage-sensitive Ca2+ channels, CoCl2 (10(-3) M) and verapamil (10(-4) M). In Ca2+-free buffer VIP, TRH and high extracellular K+ had only negligible effects, but the responses were fully restored in the presence of normal concentrations of extracellular Ca2+. In contrast to TRH, VIP had no demonstrable effect on the Ca2+-dependent action potentials of the GH4 cells.
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K M Gautvik
August 1987,
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September 1992,
Molecular and cellular endocrinology,
T Bjøro, and
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K M Gautvik
September 1982,
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T Bjøro, and
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September 1980,
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T Bjøro, and
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K M Gautvik
April 1988,
Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.),
T Bjøro, and
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K M Gautvik
January 1980,
Peptides,
T Bjøro, and
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K M Gautvik
July 1995,
General and comparative endocrinology,
T Bjøro, and
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K M Gautvik
February 1981,
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