GROWTH-HORMONE RESPONSE TO GRF AND INSULIN-INDUCED HYPOGLYCEMIA IN YORKSHIRE AND MEISHAN PIGS

Plasma glucose and porcine growth hormone (GH) responses to insulin and/or growth hormone-releasing factor (GRF) challenges were determined in Yorkshire (Y) and Meishan (MS) castrated male pigs at 140 days of age. The decline in glucose levels observed during the first 30 min after insulin injection was similar between the two breeds. In Y pigs, GH concentrations increased sharply after insulin injection. The GH response to insulin was much smaller in MS than in Y pigs (101 +/- 82 vs. 1,077 +/- 124 ng . min . ml-1, P < 0.001 after 0.30 U/kg insulin). The GH response to GRF (10 mug/kg) did not differ significantly between the two breeds. The GH response was larger after combined insulin (0.20 U/kg) plus GRF than after GRF alone in Y pigs (1,512 +/- 229 vs. 463 +/- 401 ng . min . ml-1, P < 0.05), whereas it did not differ in MS pigs (714 +/- 164 vs. 507 +/- 127 ng . min. ml-1, P > 0.10). The present data demonstrate that the GH response to insulin is dramatically altered in MS pigs. A possible explanation to this result is that somatostatin tone would not be depressed by insulin-induced hypoglycemia in MS pigs.