Plasma hormone levels in growth-retarded rats with dorsomedial hypothalamic lesions

Rats with lesions in the dorsomedial hypothalamic nuclei (DMNL rats) are hypophagic and growth-retarded. Since previous work had shown normal plasma growth hormone and insulin levels in DMNL rats we investigated the diurnal patterns of these and other hormones involved in growth. Trial 1: Rats received electrolytic DMNL or sham operations (SCON). The DMNL rats exhibited no differences from SCON rats in plasma triiodothyronine (T3), growth hormone (GH), insulin and somatomedin (SM) concentrations, Trial 2: kainic acid, a neurotoxin, was used for lesion production. Again, DMNL rats showed no deficiencies in plasma levels of T3, GH or insulin. Trial 3: In this experiment, diurnal hormone profiles were assessed. The GH profile and mean 24-hour secretion of both DMNL and SCON groups did not differ significantly. Both groups exhibited a diurnal release of T3, with the DMNL rats showing slightly higher levels. Plasma insulin rose after dark, i.e., at the onset of feeding, in SCON but not in DMNL rats; the later have a previously reported disrupted feeding rhythm. Glucose patterns were in keeping with insulin profiles. Controls showed a normal plasma corticosterone rhythm whereas DMNL rats had an altered pattern. The data suggest that deficiencies in the principal anabolic and growth-promoting hormones cannot be responsible for the retarded growth of DMNL rats.