Effects of porcine somatotropin on circulating testosterone concentrations in boars and mechanism of action

Influência do Hormônio do Crescimento na concentração de testosterona plasmática e nas características seminais de touros jovens e adultos da raça Nelore

Estudou-se o efeito do Hormônio do Crescimento bovino (bGH) sobre os parâmetros seminais e a concentração sérica de testosterona de touros da raça Nelore. Dezesseis touros foram distribuídos em um delineamento fatorial 2 x 2 (duas idades e dois níveis de r-bST), com quatro animais em cada tratamento. As aplicações de r-bST foram realizadas a cada 14 dias, totalizando nove aplicações por animal, em um período experimental de 120 dias. As coletas de sêmen foram realizadas a cada 15 dias e, para determinar as concentrações de testosterona, foram realizadas coletas de sangue a cada quatro horas, num total de 24 horas, e a cada 30 dias a partir da primeira aplicação de r-bST. O sêmen dos touros adultos tratados com r-bST apresentaram maior motilidade e vigor (P<0,05) em relação aos animais controles (79,70±11,56% vs 64,06±23,65%) e (3,80±0,88 vs 2,92±1,25), respectivamente; entretanto, as demais características seminais não foram influenciadas (P>0,05) pelo tratamento com r-bST. Os aspectos físicos do sêmen dos touros jovens não foram afetados (P>0,05) pelo tratamento com r-bST. Entretanto o tratamento com r-bST diminuiu os defeitos morfológicos menores (delgado, gigante normal, pequeno normal, globoso, cabeça isolada normal, abaxial, cauda dobrada e enrolada levemente e gota distal) em relação aos jovens não tratados (P<0,05). As concentrações séricas de testosterona foram influenciadas (P<0,05) pelo tratamento, aos 120 dias após a primeira aplicação do r-bST, e apresentaram tendência de três picos no período de 24 horas.

Effects of exogenous somatotropin (ST) on gonadal function in ruminants and swine

During the past 15 years, many investigators have examined the effects of somatotropin (ST) on growth and lactation in farm animals. Throughout this period, concerns about potential effects of ST on reproduction have been expressed. The objective of the present review will be to focus on the effects of exogenous ST on the hypothalamic-pituitary-gonadal axis. Plasma progesterone is increased when recombinant bovine (rb)ST is given to cattle, early in lactation, and also to sheep. Also, the release of progesterone from cultured swine and human luteal cells is increased by ST. Treatment with rbSt increases the numbers of small follicles, but does not increase the ovulatory rate of ruminants. Doses of ST similar to those used to increase milk production do not affect the secretion of testosterone or spermatogenesis in rams or bulls. Stimulatory and inhibitory effects of exogenous ST on reproductive function of gilts have been reported. Daily injections of porcine ST (pST) delayed puberty and expression of estrus after puberty. Daily administration of pST increased the number of small follicles, but not of medium follicles, whereas administration of pST by using a sustained release implant increased the number of medium follicles. Size and weight of reproductive organs and concentration of testosterone are not affected when pST is administered for at least 42 d. However, pST enhanced testicular development and spermatogenesis when given to neonatal boars. In summary, administration of exogenous ST at doses known to alter milk production and carcass composition may have subtle positive and/or negative effects on the reproductive systems of cattle and swine; however, these effects appear to be transient.

Effects of very high doses of human growth hormone (hGH) on the male reproductive system in the dog

The effects of very high doses of human growth hormone (hGH), pituitary derived or recombinant methionyl-hGH, on the morphology of reproductive organs and on some hormones in the male dog are described. The studies were part of a toxicological documentation of hGH. A total of 18 male dogs aged 7.5-20.5 months, from four studies were treated subcutaneously with hGH for 20-28 days at dose levels of 3, 10 or 25 IU kg-1 day-1 or 1 IU kg-1 three times weekly. Plasma levels of luteinizing hormone (LH), testosterone and prolactin were determined in one study. Organ weighing, macroscopic and histopathologic examinations of male reproductive organs at the end of the treatment period were included in all studies. Treatment with 25 IU kg-1 day-1 resulted in reduction of testis and prostate weights, degeneration of germ cells and epithelial atrophy in the testis, degenerative changes in epididymis and reduced height of the prostatic epithelium. Similar, although less severe morphological changes were observed after treatment with 10 IU kg-1 day-1. Treatment with 25 IU kg-1 day-1 also caused a marked reduction of plasma prolactin, LH and testosterone levels. These results suggest that repeated administration of very high doses of hGH interferes with the hormonal regulation of the testis in the dog.