Growth hormone secretory profiles in conscious female rats

Clark, R. G.; Carlsson, Lena; Robinson, I. C. A. F.

doi:10.1677/joe.0.1140399

Cited by 136 publications

(73 citation statements)

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“…G H levels give information on acute changes, as half-life is short. For more reliable results several measurements or a profile would be necessary, although in female rats it was observed that the G H profile has a rather constant amplitude [6,10]. Serum IGF-I levels are more important, since it gives information on the chronic effect of the exercise.…”

Section: Discussionmentioning

confidence: 99%

The effect of exercise on systemic and bone concentrations of growth factors in rats

Bravenboer

Engelbregt

Visser

et al. 2001

Journal Orthopaedic Research

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Exercise can prevent bone loss and increase bone density. Growth factors such as insulin-like growth factor-I (IGF-I) and transforming growth factor P (TGFB) are thought to be involved in the local response to mechanical loading, resulting in bone remodelling. We tested the effect of additional weight bearing during exercise on the systemic response of IGF-I and local bone response of IGF-I and TGFP.Thirty-four female Wistar rats (aged 3 months, weight 226.9 4~ 20.2 g) were randomly divided in four groups: group 1 baseline controls; group 2 sedentary controls; group 3 ran 15 min a day on a motor-driven exercise belt: group 4 ran 15 min a day with a backpack containing 40 g. The animals ran 5 days a week, for 6 weeks, with an average velocity of 16.6 i 4.4 mlmin, and a slope of 5" uphill.The serum growth hormone (GH) concentration was significantly higher in the running rats (group 3, P = 0.009) than in the sedentary controls (group 2). The IGF-I and I G F binding protein 3 (IGFBP3) levels in serum and the IGF-I levels in liver were similar in all groups. In the tibia no significant differences were observed in IGF-I, IGFBP3 and TGFP concentration. In the humerus, the IGF-I concentration was lower in the running rats (group 3 ) than in the sedentary controls ( P = 0.04), but it was higher in the rats that ran with additional weight than in those without ( P = 0.009). The TGFP concentration in the humerus was lower in both group 3 ( P = 0,001) and 4 (P = 0.03) than in the sedentary controls.The effects in bone caused by mechanical stimulation cannot be explained by changes in serum IGF-I and IGF-I produced in the liver. The concentrations of IGF-I and TGFP in bone appeared to be modulated by running exercise. 0

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Section: Discussionmentioning

confidence: 99%

The effect of exercise on systemic and bone concentrations of growth factors in rats

Bravenboer

Engelbregt

Visser

et al. 2001

Journal Orthopaedic Research

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“…Rat GH and PRL were assayed by RIA using reagents supplied by NIDDK as previously described (Clark et al 1987, Carmignac & Robinson 1990). …”

Section: Analysis Of Pituitary Extractsmentioning

confidence: 99%

Increased lactotrophs despite decreased somatotrophs in the dwarf (dw/dw) rat: a defect in the regulation of lactotroph/somatotroph cell fate?

Tierney

Robinson²

2002

Journal of Endocrinology

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The dwarf (dw/dw) rat differs from all other rodent models of GH deficiency in that its pituitary prolactin (PRL) content is normal or even increased. We have now studied this throughout postnatal development, using a combination of immunocytochemistry, RIA and fluorescenceactivated cell sorting (FACS) and analysis. Compared with normal Albino Swiss (AS) rats, adult dw/dw rats showed a profound reduction in pituitary GH content accompanied by increased PRL content, significantly so in females (AS vs dw/dw; P<0·01). Somatotroph hypoplasia was evident in the adult dw/dw rats, with most GH +ve cells showing weak immunostaining, whereas many more strongly stained PRL cells were evident in pituitary sections from dw/dw rats. FACS analysis confirmed both somatotroph hypoplasia and relative lactotroph hyperplasia in dw/dw rats at all ages studied (9-144 days); the difference in somatotrophs increased with age whereas the difference in lactotrophs declined with age. At 9 days, the percentage of lactotrophs was 10-fold higher in dw/dw rats than in AS rats. Young dw/dw rats also had a higher proportion of mammosomatotrophs than AS rats, although this difference disappeared as the mammosomatotroph proportions increased with age in both strains. GHRH released GH from both dw/dw and AS cells maintained in culture for 5 days. The sensitivity to GHRH and the amount of GH released was lower in the dw/dw cultures, mostly explained by their fewer GH cells and lower initial GH content. GHRH increased cAMP in AS but not in dw/dw cultures, even when these were greatly enriched for dw/dw somatotrophs by FACS sorting prior to culture. These results suggest that GHRH-induced cAMP stimulation is required for trophic effects on GH synthesis and somatotroph proliferation, but is not required for GHRH-stimulated GH release. The inverse changes in somatotroph and lactotroph numbers suggest that the dw/dw mutation disturbs the mechanism that specifies and retains appropriate numbers of somatotrophs in their differentiated state, and results in a higher proportion of the remaining cells progressing to lactotrophs. The dw/dw phenotype is thus not confined to somatotrophs.

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“…Recent studies indicate that the frequency of administration is important as regards the effects of the hormone. The endogenous growth hormone secretion is highly pulsatile; in the rat the secretory bursts occur at approximately 3-hour intervals (Tannenbaum and Martin 1976, Ed& 1979, Clark et al 1987). Jansson et al (1982) found that the Iongitudinal bone growth and weight gain in hypophysectomized rats increased when equal daily doses of growth hormone were given in 2-8 daily injections rather than in one single injection.…”

Section: Discussionmentioning

confidence: 99%