Pituitary growth hormone release and gene expression in cafeteria-diet-induced obese rats

In human obesity as well as in rat obesity models a decrease in spontaneous and stimulated GH secretion has been a constant finding. The presence of a decreased pituitary GH synthesis in diet-induced obese male rats was investigated and its possible relationship with obesity-related changes in peripheral hormones was analyzed. Cafeteria-diet-overfed obese male Wistar rats with body fat percentage above 30% had a significantly decreased pituitary GH mRNA transcript level assessed by both Northern blot and in situ hybridization, and a lower pituitary GH protein level as demonstrated by immunocytochemistry. The GH transcript level correlated negatively with the serum leptin and positively with the IGF-I concentration. No differences in circulating tri-iodothyronine, non-fasting insulin and corticosterone levels were found between overfed and control rats. GH release by cultured pituitary cells from overfed rats was comparable to that by cells prepared from control rats. In contrast, incubation of normal pituitary cells with serum from overfed rats for 3 days gave a significantly lower GH release than after incubation with serum from non-obese rats. In conclusion, cafeteria-diet-induced obese male Wistar rats have a decreased pituitary GH gene expression and a modifiable GH release in in vitro experiments. A possible role for peripheral circulating factors, like leptin and IGF-I, in decreasing the pituitary GH synthesis and release in obese rats is discussed.