抄録
Effects of VIP on cyclic nucleotides formation in various central nervous tissue of rat were examined. The tissue including anterior pituitary prepared from rat brain after decapitation were incubated in Krebs-Ringer bicarbonate buffer containing 0.1% glucose and 0.1% bovine serum albumin and synthetic hormone to be tested. Cyclic AMP was determined with competitive protein binding assay and cyclic GMP was assayed by specific radioimmunoassay system. Hormones released into incubation medium were determined with radioimmunoassay system specific for each hormone.
Synthetic VIP increased cyclic AMP concentration, not cyclic GMP concentration, in brain medulla, hypothalamus, pons and anterior pituitary, but not in brain cortex, cerebellum and posterior pituitary. Minimum effective dose of synthetic VIP was 1μg/ml. Other synthetic gastrointestinal hormones (Gastric Inhibitory Peptide, Motilin, Bombesin, Substance P and Gastrin) did not affect cyclic AMP concentrationin every tissue. Synthetic VIP strongly stimulates cyclic AMP production, but it (in the concentration between 100μg and 10μg) did not stimulate hormone release into incubation medium from anterior pituitary (GH, TSH, LH, FSH and Prolactin) as well as from hypothalamus (TRH, LHRH and Somatostatin).
Although somatostatin decreased basal cyclic AMP level in anterior pituitary and inhibited TRH and PGE stimulation of cyclic AMP formation, it did not inhibit stimulatory effect of synthetic VIP on cyclic AMP formation in anterior pituitary and hypothalamus, and also propranolol (10-4M) did not.
These results suggest strongly that VIP may have some physiologic actions on specific portions of rat central nervous system and, in anterior pituitary and hypothalamus, its action may be different from stimulation of hormone release from these two tissues, and those may indicated the possibility of presence of intracellular compartment of functioning cyclic AMP.
