Hypothalamic neuropeptide Y mRNA in pregnant, lactating and suckling rats.

Blood glucose, plasma insulin and luteinizing hormone levels were studied in pregnant wistra rats and those in early and late stages of lactation. NPY mRNA was also measured in whole hypothalamic tissue of these rats which were either fed ad libitum or food deprived to 80% of the relative controls. When fed ad libitum, hypothalamic NPY mRNA was not significantly elevated in the pregnant rats (111 +/- 2.1%). By the 5th and 4th days of lactation the mRNA had increased progressively (141 +/- 4.7% of control, p<0.01; 186 +/- 9%, p<0.001) respectively. Blood glucose levels were unchanged in pregnancy and lactation, however, insulin levels dropped significantly by the ]4th day of lactation (control 322.3 +/- 3.2; lactating 298.6 +/- 4.8 pmol/l; p<0.05). Luteinizing hormone was significantly reduced in the lactating rats (control 2.2 +/- 0.21, lactating 0.81 +/- 0.2 ng/ml;p<0.05). In food restriction, NPY mRNA was increased moderately in the non-pregnant state and enormously in late lactation (non-pregnant 157 +/- 21%, lactating 333 +/- 35%, p<0.001). In a lactation, blood glucose was unchanged while plasma insulin and LH were reduced to 20% and 50% of controls respectively (insulin: control 110.3 +/- 2.0; lactating 18.3 pmol/l; LH. control 1.3 +/- 0.1; lactating 0.59 +/- 0.4 ng/ml p<0.01). Orexigenic effect of hypothalamic NPY is possibly responsible for the hyperphagia in lactating. Food restriction and lactation had additive lowering effect on plasma insulin but an additive increase on hypothalamic NPYmRNA. NPY message may be partially responsible for the anovulatory effect of lactation.