VIP-stimulated cyclic AMP accumulation in the suprachiasmatic hypothalamus.

The effect of exogenous vasoactive intestinal peptide (VIP) on the accumulation of cyclic AMP in the isolated suprachiasmatic hypothalamus prepared from rats sacrificed at midsubjective day (CT6), subjective dusk (CT12) and midsubjective night (CT18) was determined. VIP (2 microM) caused a transient, 2.5- to 3.4-fold increase in cyclic AMP which peaked 5 minutes after the addition of VIP and returned to prestimulation values by 10 minutes. The effect of VIP was dose dependent between 0.1 and 10 microM. Cyclic AMP content, both before and after VIP stimulation, was slightly but significantly higher in rats sacrificed at CT6 compared to those sacrificed at CT18; however, the degree of stimulation was similar at all three circadian times.