Adenylyl cyclase stimulation by VIP in rat seminal vesicle membranes

Vasoactive intestinal peptide (VIP) stimulated adenylyl cyclase activity in membranes from rat seminal vesicle. GTP potentiated the stimulatory effect of VIP so that it was routinely included at 10 microM. The stimulation of adenylyl cyclase by VIP was time and temperature dependent. The response was linear with time up to 15 min at 30 degrees C. Half-maximal adenylyl cyclase activation (in the presence of 10 microM GTP) was achieved at 3.0 nM VIP. The enzyme activity increased about 150% with respect to basal values at the maximal VIP concentration tested (1 microM). The relative potency of peptides upon stimulation of adenylyl cyclase activity was: VIP greater than helodermin greater than peptide histidine isoleucinamide greater than rat growth hormone-releasing factor. Other agents like GTP (0.1 mM), GppNHp (0.1 mM), forskolin (0.1 mM) and sodium fluoride (10 mM) increased the adenylyl cyclase activity 1.8-, 4.4-, 6.7- and 2.4-fold, respectively. Taken together, the presence of VIP in nerve terminals innervating the seminal vesicle of rats and the existence of VIP receptors coupled to adenylyl cyclase strongly suggest a physiological role for this neuropeptide in the modulation of seminal vesicle cell function.