Endocrine Abstracts

Mice overexpressing growth hormone (GH) have about two-fold higher IGF-I and clear increases in body and organ weights. Moreover, administration of GH to hypophysectomised or dwarf mice has been shown to increase IGF-I. Data on the short term effects of exogenous administration of rhGH in normal rodents remain scarce.

Therefore, we measured IGF-I before and after one week of GH-treatment in 10-week-old female mice, injected daily with two different doses of rhGH: 0.5 mg/d (GH-1) and 0.125 mg/d (GH-2). Controls (C) received equal volumes of 0.9% NaCl.

Liver, heart, kidneys, adrenals, perirenal and abdominal fat pads were excised and weighed.

After one week, mice were heavier with both doses of GH. Bodyweight (BW) increased by 6% under high dose GH-administration (P<0.05), whereas control mice did not show any BW-gain. Liver weights were significantly higher in both GH-groups compared to control groups (GH-1: 1.27±0.06 g; GH-2: 1.39±0.12 g; C: 1.15±0.03 g P<0.001). Weights of kidney, heart and adrenals were higher under both GH doses compared to controls, but only increases in heart weight of GH-2 reached statistical significance (P<0.05). No differences were present in perirenal fat pad weights, whereas abdominal fat pad weights were dramatically lower by about 50% in GH-1 when compared to controls (P<0.05). Surprisingly, neither GH-1 nor GH-2 showed significant change in IGF-I levels, when compared to control animals (GH-1: 445±104 ng/ml; GH-2: 576±54 ng/ml; C: 435±136 ng/ml; GH-1 and GH-2 versus C P=0.9 or 0.57, respectively). In GH-1 group, serum IGF levels were unchanged before and after one-week of GH treatment (P=0.46).

In conclusion, administration of supraphysiological doses of GH to healthy adult mice led to profound changes in BW, liver weight and visceral adipose tissue. However, despite these effects we could not detect any change in IGF-I. Our data suggests that IGF-I is not a suitable pharmacodynamic marker of GH-action in ordinary rodents.