Neuropeptide Y enhances LHRH binding to rat gonadotrophs in primary culture

Abstract

Incubation of dispersed adenohypophyseal cells from intact male rats with Neuropeptide Y (NPY) or Peptide YY (YY) at 21°C increased maximal 125I LHRH a binding (Bmax) by about 50%. In presence of 10 −7 M NPY, Bmax calculated from saturation isotherm curves was 15.3 ± 1.9 fmolex × mg −1 proteins, as compared to 10 ± 1 fmoles × mg −1 in control incubates. The increase was dose dependent with an EC 50 of 6.3 ± 1.8 10 −10 M NPY. Preincubation of the cells with pertussis toxin (PT, 15 ng/ml) for 24 h abolished the effect, suggesting coupling of NPY receptors to Gα o or Gα i proteins. NPY 10 −7 M inhibited basal and Forskolin 10 −5 M stimulated intracellular cyclic AMP formation by 31.9 ± 3.4% and 30.6 ± 2.3% respectively. Desensitization of protein kinase C by overnight preincubation of the cells with 10 −6 M phorbol ester (PMA) did not interfere with the effect of NPY. In contrast, W7, a calmodulin inhibitor, as well as H7, a protein kinase C inhibitor with a relatively wide spectrum, suppressed the effect of NPY with IC 50 of 1.4 ± 0.6 10 −6 M and 2.2 ± 0.5 10 −5 M, respectively. Taken together, these results suggest that NPY is able to control unmasking of a cryptic LHRH receptor pool in pituitary cells by a process dependent upon both GTP binding proteins and calmodulin dependent protein kinase.