Effect of sex steroids on plasma C-type natriuretic peptide forms: stimulation by oestradiol in lambs and adult sheep

Abstract

Although C-type natriuretic peptide (CNP) is crucial to postnatal endochondral growth, roles for the hormone in pubertal bone growth and the physiological effects of sex steroid substitution on CNP synthesis are not known. Using a plasma marker of CNP tissue synthesis (amino-terminal proCNP, NTproCNP), we have studied the effect of exogenous oestrogen (E 2 ) or testosterone (T) on plasma CNP forms and bone alkaline phosphatase (bALP) in pre-pubertal lambs.Responses to E 2 in non-cycling adult ewes were also studied. In 15-week-old intact ewe lambs, E 2 promptly increased plasma NTproCNP and CNP (P!0 . 001) to peak on day 2, and bALP (P!0 . 001 peaking on day 7), whereas no significant stimulation in response to T was observed in male lambs. Linear bone growth and live weight were unaffected. In adult anoestrous ewes, basal concentrations of CNP forms and bALP were lower than in ewe lambs, in keeping with skeletal maturity, but adults responded similarly to E 2 . Prompt and sustained increases in NTproCNP and CNP, and a later threefold rise in bALP (all P!0 . 001), were induced by E 2 . Possible contributions to these increases in plasma CNP forms by reproductive tissues (a known site of E 2 -induced CNP expression) were excluded by showing similar E 2 -induced CNP responses in adult ewes after surgical removal of reproductive tissues. These results are the first to show that E 2 stimulates plasma CNP forms and bALP in lambs and adult sheep and raise the possibility that CNP also participates in bone formation in the mature skeleton.

Serum total and bone alkaline phosphatase levels and their correlation with serum minerals over the lifespan of sheep

“…The measurement of the serum BALP concentration was performed with a commercial immunoassay kit (Ostase ® , Beckman Coulter, Fullerton, CA, USA) using an automated biochemistry analyser (Access Immunoassay System ® , Beckman Instruments Inc.) based on chemical luminescence principles, assayed as previously described (Prickett et al, 2008). All samples were measured in duplicate and the mean values were calculated.…”

Regulation of C-type natriuretic peptide expression

“…The source of the elevated CNP, while not definitively identified, was thought likely to be derived from osteoblasts in bone tissue [70]. In marked contrast to the finding of a positive relationship between testosterone and CNP in pre-pubertal boys [65], Prickett et al observed no effect of testosterone administration on CNP in male lambs, a species difference in CNP regulation that the authors speculated could be related to the timing of testosterone intervention and the stage of pubertal maturation [70]. These studies point to the possibility that the influence of steroids on bone growth could be mediated, at least in part, through their regulation of CNP synthesis.…”

“…Furthermore, uterine CNP and CNP transcription were observed to increase with the administration of exogenous estradiol to ovariectomized mice [1]. A steroid hormone-responsive consensus sequence has not yet been identified in the CNP promoter [70,89], suggesting that the observed effects of steroids on CNP expression could be secondary to their effects on the transcription of other proteins.…”

“…Using plasma levels of amino-terminal pro CNP (NT-proCNP) as a biomarker for hormonal regulation of CNP in the cartilage growth plate, Olney et al [65] showed evidence that the positive effects of growth hormone and testosterone on bone growth at puberty could be due in part to their up-regulation of CNP production in the growth plate at this time. Also using NT-proCNP as a plasma biomarker of CNP synthesis, Prickett et al [70] showed that exogenous estradiol administered to female lambs and adult sheep significantly increased CNP expression compared with control animals. The source of the elevated CNP, while not definitively identified, was thought likely to be derived from osteoblasts in bone tissue [70].…”

“…Also using NT-proCNP as a plasma biomarker of CNP synthesis, Prickett et al [70] showed that exogenous estradiol administered to female lambs and adult sheep significantly increased CNP expression compared with control animals. The source of the elevated CNP, while not definitively identified, was thought likely to be derived from osteoblasts in bone tissue [70]. In marked contrast to the finding of a positive relationship between testosterone and CNP in pre-pubertal boys [65], Prickett et al observed no effect of testosterone administration on CNP in male lambs, a species difference in CNP regulation that the authors speculated could be related to the timing of testosterone intervention and the stage of pubertal maturation [70].…”