The influence of growth hormone injections on the endocrine and metabolic status of gilts

Twelve Yorkshire x Landrace prepubertal gilts were assigned equally to treatments involving daily injections of either porcine growth hormone (GH, 90 micrograms/kg) or vehicle buffer from 150 to 159 d of age. Blood samples were obtained every hour from 0600 hr at 153 d until 0500 hr at 154 d of age, inclusively. At 0800 hr on 154 d, gilts received an injection of 500 IU PMSG, followed 96 hr later by 250 IU hCG. Gilts were slaughtered at 163 d and the ovaries recovered for an assessment of the ovarian response to the gonadotrophic stimulation. Five control gilts (83%) exhibited a normal ovulatory response but only one GH gilt (17%) was so designated (P less than 0.05). There was no apparent effect of treatment on serum concentrations of LH, FSH or cortisol. Growth hormone treatment reduced serum concentrations of T4 (P less than 0.001) and prolactin (P less than 0.02), but increased serum GH (P less than 0.001), T3 (P less than 0.06), insulin (P less than 0.001) and glucose (P less than 0.001). Serum concentrations of free fatty acids (FFA) were not significantly altered by exogenous GH. The concomitant elevation of serum insulin and glucose suggests that an insulin-resistant state was induced which, if evident at the ovarian level, may be a factor mediating the adverse effects of exogenous GH on ovarian function. The data presented also suggests that circulating concentrations of thyroid originating hormones are altered by exogenous GH.