Byeongki Kim

Publication Date


Document Type


First Advisor

Conway, Sonya

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Biological Sciences


Clonidine; Steroid hormones; Sexual dimorphism (Animals); Somatotropin; Hormones; sex


The significance of gonadal steroids in the development of the sexually dimorphic pattern of growth hormone (GH) secretion in the rat was studied by examining the influence of prepubertal gonadectomy and postoperative steroid replacement on the modulation of GH secretory responses to a2-adrenergic (CX2) stimulation and GH feedback. The responses to the c»2-stimulation and feedback inhibition were tested at 75-80 days of age by administering clonidine (CLON) intravenously (iv) and oGH into the third ventricle (ivt) three hours before CLON. To examine if the responses are of developmental significance, similar tests were conducted in animals gonadectomized postpu- bertally. This study showed the presence of sexual dimorphism in the GH secretory response to the (X2-stimulation and GH feedback; males displayed higher sensitivities to both stimuli compared to females. Testosterone (T) may be the testicular factor required for establishing male sensitivity and may be active as early as day 25. Further, the effect of T could not be duplicated by estrogen (E). However, E exerted a potentiating effect in the male system after 30 but not 25 days of age, suggesting the Importance of the prepubertal exposure to the testes between days 25 and 30. Because sensitivity to stimuli was reduced by gonadectomy before and after puberty, continuous exposure to T is necessary to establish the male pattern of GH responses. The significance of prepubertal ovarian steroids in the development of the characteristic female responses was also examined. The profile of female responses to c^- stimulation and GH feedback was similar to that of males in day 25-OVXed animals. The sensitivity to stimuli was decreased in day 30-OVXed animals and completely eliminated in animals OVXed in adulthood, suggesting that the female response is established by prepubertal and/or pubertal ovarian steroids. Continuous exposure to P from day 25 was required for suppressing sensitivity to 0C2- agonist and similar exposure to E was necessary for eliminating feedback sensitivity. On the other hand, E potentiated both sensitivities in day 30-OVXed animals, suggesting that the suppressive effect of P seems to be dominant over the E effects after day 30.


Includes bibliographical references (pages [106]-134)


vi, 142 pages




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