Changes in the hypophysial-gonadal axis during the onset of puberty in young bulls

Abstract

The objectives of this study were to determine the extent of changes in concentrations of testosterone, growth hormone (GH) and insulin-like growth factor I (IGF-I) concentrations in blood plasma and to characterize the respective plasma-binding proteins of these two peptides during the onset of puberty in male calves. The jugular veins of six male Holstein calves (11-weeks-old) were catheterized and blood was collected every 3 days (one sample every 30 min for 8 h). Hormone concentrations in plasma were determined by specific radioimmunoassay. After incubation with [125I]IGF-I, IGF-I-binding proteins (IGFBPs) were separated by gel filtration; radioactivity was determined in each fraction. Western ligand blotting using radiolabelled hormones as ligand was also used to characterize the IGF-I- and GH-binding proteins in plasma. Puberty was characterized by a rapid (in 1 or 2 days) increase in mean concentrations of testosterone in plasma (from 0.5 to > 2 ng ml-1) and a pulsatile release of the hormone. During puberty, IGF-I concentrations also increased rapidly in 8-10 days from +/- 50 ng ml-1 to > 150 ng ml-1, whereas concentrations of GH in plasma remained relatively stable during the experimental period. A significant correlation was observed between IGF-I and testosterone concentrations (r = 0.77; P < 0.001) throughout the experimental period. Three different IGF-I-binding protein fractions with apparent molecular masses of > 200, 150-170 and 45-65 kDa were found in plasma using gel filtration.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of short-term feed restriction on milk yield and composition, and hormone and metabolite profiles in mid-lactation Sarda dairy sheep with different body condition score

“…All samples were analyzed in a single assay with a limit of detection of 1 ng/mL. Plasma concentration of IGF-I was evaluated by RIA according to the method described by Renaville et al (1993).…”

Dissociation of increases in plasma insulin-like growth factor I and testosterone during the onset of puberty in bulls

“…During this period, testosterone is released episodically and plasma concentrations of IGF-I increase strikingly, concomitant with an increase in mean plasma concentration of testosterone. A positive corre¬ lation was noted between the concentrations of these two hormones for bull calves during this physiological step (Renaville et al, 1993). Moreover, as in humans (Smith et al, 1993), baboons (Crawford et al, 1994) and pigs (Lee et al, 1991a), in cattle, the transition from prepubertal to mature male is characterized by a marked increase in concentrations (Renaville et al, 1993).…”

“…A positive corre¬ lation was noted between the concentrations of these two hormones for bull calves during this physiological step (Renaville et al, 1993). Moreover, as in humans (Smith et al, 1993), baboons (Crawford et al, 1994) and pigs (Lee et al, 1991a), in cattle, the transition from prepubertal to mature male is characterized by a marked increase in concentrations (Renaville et al, 1993). However, information on the possible link between IGF-I and testosterone synthesis during this physiological step is contradictory.…”

“…The onset of puberty has been shown to be a complex synergism between sex steroids and insulin-like growth factor I (IGF-I) in humans (Metzger et al, 1994), sheep (Lord et al, 1991) and in cattle (Renaville et al, 1993). During this period, testosterone is released episodically and plasma concentrations of IGF-I increase strikingly, concomitant with an increase in mean plasma concentration of testosterone.…”

Relationships of thyroid hormones, IGF-I and testosterone in breeds of ram lambs with low and high prolificacies

“…Puberty in the male mammal is manifested by developmental processes at the hypothalamic-pituitary-gonadal axis (Amann 1983) with episodic release of testosterone (Renaville et al 1993). Testosterone may be considered as a primary regulator for other major physiological changes during this period.…”