Growth hormone treatment increases oestrogen receptor concentration in the guinea-pig uterus

Growth hormone does not act as a body growth-promoting hormone during the postnatal period in the guinea-pig. To determine whether it affects uterine and mammary growth, guinea-pigs of 8-9 weeks of age were treated with either recombinant bovine GH (bGH; 0.5 mg per animal) or vehicle for 10 days. Uterine and mammary weights were not changed by treating the animals with bGH. The amount of available cytosolic oestradiol receptor per unit of uterine weight or DNA content, or in whole uteri was increased in bGH-treated animals (7.3- to 14.0-fold) when compared with controls. The nuclear uterine oestradiol receptor concentration was 3.3- to 6.7-fold higher than in controls. The dissociation constant values did not differ between control and bGH-treated animals, suggesting that uterine oestradiol receptors are regulated by GH through changes in the number of binding sites rather than alteration of their binding affinity. Mammary growth and oestradiol receptor levels were unaffected by bGH treatment. The results of this investigation demonstrate that injected bGH selectively affects the oestradiol receptor level in guinea-pig uterine tissue.