Effects of repetitive administration of growth hormone-releasing hormone on growth hormone secretion, insulin-like growth factor I, and bone metabolism in postmenopausal women.

This study sought to determine whether GH response to synthetic GHRH was impaired in 13 postmenopausal (55-71 years) as compared with that in 8 eugonadal women and whether IGF-I and bone metabolism were consequently depressed. Thereafter, the effects of daily iv injections of 80-micrograms GHRH-44 for 8 days were studied in the same postmenopausal group. In addition to significantly higher basal IGF-I and osteocalcin levels (P less than 0.005) in eugonadal as compared with the postmenopausal women, the administration of one GHRH-44 injection resulted in significantly higher 120-min postinjection GH maximum peak and cumulative responses in the former group as well (P less than 0.005). Highly significant correlations were observed between 17 beta-estradiol plasma levels and either GH maximum peak or cumulative responses to GHRH-44 when both groups were pooled together, but not when considered independently. In postmenopausal women, a correlation was found between both age and duration of menopause and GH responses. Repeated GHRH-44 injections in postmenopausal women induced a significant increase in GH response (P less than 0.001) as well as in IGF-I levels from day 4 to 8. No phospho-calcium parameters were modified except for a significant rise in osteocalcin from day 2 to 8. These data indicate an age-related loss of sensitivity of somatotrope cells to GHRH-44 in postmenopausal women, partly corrected by repeated daily GHRH-44 injections. As a consequence of the GHRH-induced increase in GH secretion, IGF-I was also enhanced and may be responsible for a stimulatory effect on bone formation, as shown by the osteocalcin increase, uncoupled from bone resorption.

1-Year controlled randomised trial of prevention of early postmenopausal bone loss by intranasal calcitonin.

79 women who had been menopausal for less than 36 months and who had not received any form of treatment to prevent bone loss were randomly assigned to a 12-month regimen of calcium 500 mg/day or calcium 500 mg plus intranasal salmon calcitonin 50 IU/day for 5 days per week. After 12 months of treatment bone mineral density had decreased in the calcium-only group by a mean of 3.16 (SEM 0.6)% (p less than 0.01) but had increased in the calcium plus calcitonin group by 1.38 (0.8)% (NS). The difference in response between the two treatment groups was also highly significant (p less than 0.01), as was the difference between values for hydroxyprolinuria/creatininuria (p less than 0.01). Endogenous calcitonin levels rose significantly in the calcium group but remained unchanged in calcitonin-treated patients. Treatment by calcitonin and calcium was not followed by increased secretion of parathyroid hormone. The findings suggest that intranasal calcitonin can counteract early postmenopausal bone loss.

Subcellular fractionation of pituitary neurointermediate lobes: revelation of various basic proteases.

Homogenates of rat neurointermediate lobes were purified by centrifugation on a Percoll gradient. Lysates of the Percoll gradient fractions were incubated with a synthetic octapeptide and pentapeptide substrate (N-acetyl Lys-Arg-Tyr-Asn-Leu-Thr-Ser-Val-amide and N-acetyl Lys-Arg-Tyr-Asn-Leu-amide), and enzymatic characteristics were compiled. Early assays on nonamidated forms revealed carboxypeptidase activity, whereas with the amide derivatives no carboxypeptidase activity could be detected. These amide substrates were therefore used in all subsequent incubations. High levels of a Leu/Thr and Lys/Arg cleavage were present in fractions almost throughout the Percoll gradient. Cleavages at Tyr/Asn, Thr/Ser, and Arg/Tyr were localized at different regions of the Percoll gradient. Surprisingly, none of the five enzymatic activities appear to be localized in the secretory granule fractions as defined by the presence of immunoreactive beta-endorphin in the gradient. All of the five proteolytic activities have a basic pH optimum (pH 8-9), and four of them seem to be thiol proteases, as categorized by inhibitor studies. The fifth one, namely the Try/Asn cleavage, is more likely to be due to a metalloendopeptidase, since it is activated by Zn2+ and Co2+.

Enzymatic maturation of pro-opiomelanocortin by anterior pituitary granules. Methodological approach leading to definite characterization of cleavage sites by means of high-performance liquid chromatography and microsequencing.

The coupling of high-performance liquid chromatography, gel-permeation, and reversed-phase chromatography with microsequencing proved to be advantageous for the unambiguous determination of specific sites in pro-opiomelanocortin, cleaved by secretory granule lysates of pig anterior pituitary. This system allows the unambiguous identification of a major chymotrypsin-like enzyme activity, optimal at pH 8.0, in the granule preparation, with a specificity directed towards some Phe decreases X and Tyr decreases X cleavage sites. The approach used emphasizes the necessity to use methodologies leading to the unambiguous determination of conversion activities.