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BR Pal, T Marshall, C James, and NJ Shaw

There is no consensus between Authors on the definition of a replete or deficient vitamin D state. Our aim was to describe a suitable method that could be used to compare vitamin D data in subject groups with small or large numbers. Two hundred and forty indigenous asymptomatic, non-pregnant adult subjects recruited from a single-consultation outpatient attendance with normal biochemistry, represented a sample of our inner city district population. 25-hydroxyvitamin D (25,OHD3) levels were measured to illustrate the effects of season, sex and ethnic group on vitamin D levels and subjected to distribution analysis. This method quantifies as a percentage the distribution of 25,OHD3 concentrations (observed concentration, OC) in pooled group data. The data can be expressed as distribution frequency domains or cumulative frequency ogives (0-100%) or transformed into discrete linear probits, amenable to regression analysis. An estimate of the OC50 (mid-point) and upper (either OC75 or OC95) or lower (either OC25 or OC5) range or at any other frequency between subject groups can be compared. A marked difference in 25,OHD3 levels between Asian and non-Asian asymptomatic adult subjects was seen during both seasons. 25,OHD3 deficiency was defined as at or below the OC25 for the non-Asian group (for both sexes: winter < 13.36 ng/ml, summer <13.38 ng/ml). The majority of Asians of both sexes were 25,OHD3 deficient (winter 94%, summer 82%). The distribution analysis provides an easy technique to compare 25,OHD3 status of different subject groups, allowing the description of populations using either longitudinal or cross-sectional data. This method may offer a way of describing 25,OHD3 deficiency between observers worldwide.

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S Ramaswamy, C R Pohl, G R Marshall, and T M Plant

This study examined the ontogeny of the testicular testosterone response to precocious pulsatile LH stimulation in the juvenile rhesus monkey. LH stimulation was achieved with an i.v. infusion (one pulse every 3 h) of either single-chain human (sch)LH, administered alone or in combination with recombinant human (rh)FSH, or recombinant monkey (rm)LH in combination with rmFSH. Homologous gonadotropin treatment resulted in an adult profile of circulating mLH concentrations. The schLH infusions produced a similar pulsatile pattern in circulating LH with peak concentrations of approximately 5 IU/l. Although a robust testicular testosterone response was observed after 24 h of intermittent LH stimulation, surprisingly testosterone release at this time was continuous. The apulsatile mode of testosterone secretion, however, did not persist, and a switch to an unequivocal episodic mode of secretion, comparable to that observed in adult monkeys, occurred by day 4 of LH stimulation. FSH did not influence the pattern of the testosterone response. We conclude from these findings that progenitor Leydig cells in the primate testis are able to respond rapidly to a physiological LH stimulus. While the cell biology underlying the switch from a continuous to a pulsatile mode of testosterone secretion remains unclear, we suggest that this phenomenon may be related to the hypothesis that episodic testosterone secretion is required for the operation of the neuroendocrine axis governing testicular function.

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In post-partum lactating rats, sucking by the young was associated with high prolactin release and maintenance of lactation but severe inhibition of LH and FSH release and suspension of oestrous cycles. Shortly after the pups were removed on day 22 post partum, LH and FSH release returned to normal and oestrous cycles resumed. Twice-daily injections of ergocornine methanesulphonate (ERG) into mothers beginning at 5 or 7 days post partum, resulted in sustained inhibition of prolactin release and diminished milk secretion. By frequent exchange of pups between control and ERG-treated mothers, it was possible to maintain vigorous sucking and almost normal pup growth despite low serum prolactin levels and diminished lactation. In these rats, serum levels of LH remained low during 11 or more days of treatment with ERG, but serum FSH was consistently higher than in untreated control mothers. After 11 or more days of ERG treatment, most rats showed a return to normal LH and FSH release and resumption of oestrous cycles. These results suggest (a) that the sucking stimulus rather than high prolactin levels in the circulation is mainly responsible for inhibition of LH and FSH release during the first 11 days post partum, (b) that the sucking stimulus acts to increase prolactin and inhibit LH release by separate hypothalamic mechanisms, and (c) that administration of ERG results in diminished prolactin release and lactation, and in increased release of FSH and subsequently of LH with earlier resumption of oestrous cycles.

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The effects of clomiphene citrate were studied in nine normal men, in three patients with partial panhypopituitarism, and in four patients with isolated gonadotrophin deficiency. The administration of this drug to the normal subjects in a dosage of 3 mg/kg/day for 10 days resulted in a mean rise in serum luteinizing hormone (LH) of 107%, in plasma 17β-hydroxyandrogens (17-OHA) of 114%, and in plasma total cortisol of 86%. The rise of testosterone concentration in normal subjects was associated with a doubling of the non-protein bound fraction, and also with increased binding of testosterone to sex hormone-binding globulin (SHBG). In contrast, plasma non-protein bound and urinary unconjugated cortisol remained unchanged. The percentage of plasma cortisol not bound to protein fell, indicating that the rise in total plasma cortisol was secondary to increased protein binding. This was confirmed by finding increased binding of both cortisol and testosterone to their specific binding globulins at 1 °C, due apparently to increased concentrations of SHBG and corticosteroid-binding globulin after clomiphene administration. All the responses to clomiphene were prevented by simultaneous administration of fluoxymesterone in two normal subjects.

All the hypopituitary patients showed no rise of LH, 17-OHA or cortisol. The hypogonadotrophic patients, however, showed a normal total cortisol rise.

It is suggested that clomiphene has two actions. First, it interferes with the hypothalamic feed-back mechanisms for testosterone, resulting in increased LH secretion, and secondly it has an oestrogen-like effect in stimulating production of steroid-binding globulins.

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Human luteinizing hormone (LH) was given by intravenous infusion to four normal male volunteers. The disappearance of immunoreactive LH from serum followed a single exponential decay, the mean half-life being 136 min. The effect on the testis of the infused LH was variable. Despite high serum LH levels being achieved, only one subject showed a clear increase in circulating 17β-hydroxyandrogen (17-OHA) levels, the other subjects showing little change in the immediate post-infusion period. All subjects had low 17-OHA levels in the period 24–36 h after the infusion. No consistent changes in serum follicle-stimulating hormone levels occurred during or after the infusion.

This suggests that other factors besides LH are necessary to produce maximal testosterone secretion by the testis, and may also be concerned in controlling the diurnal variation of testosterone.

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M T Dattani, P C Hindmarsh, C G D Brook, I C A F Robinson, and N J Marshall


The effects of a recombinant human GH-binding protein (rhGHBP; amino acids 1–238) on GH stimulation of rat Nb2 lymphoma cells were examined with an eluted stain assay system (ESTA). This precise bioassay utilizes the colorimetric reduction by stimulated Nb2 cells of a yellow tetrazolium salt (3-[4,5-dimethyl-thiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) to a purple formazan as its end-point. The use of a lactogenic bioassay allowed the investigation of hGHBP specificity for human GH (hGH) as opposed to prolactin. rhGHBP inhibited pituitary hGH bioactivity in a dose-dependent manner. No significant inhibition of prolactin or ACTH bioactivity occurred. It was confirmed that recombinant 20 kDa hGH also stimulated the Nb2 cells and that its relative potency was ∼ 10% of that of pituitary-derived hGH. Stimulation by 20 kDa hGH was also inhibited by rhGHBP. The highly quantitative ESTA system demonstrated that the binding protein inhibited in a competitive manner. hGH activation of the Nb2 cells did not appear to be governed by a Michaelian first-order reaction. As might then be anticipated, the concentration of rhGHBP required for 50% inhibition of GH bioactivity (IC50) changed with agonist concentrations for both 20 kDa and 22 kDa hGH. However, with equimolar concentrations of these two isohormones, the IC50 of the binding protein was virtually identical. Potentiation of hGH bioactivity in vivo by low concentrations of hGHBP has been reported but was not observed in our in vitro system when tested over a wide range of binding protein concentrations.

In conclusion, the ESTA bioassay system permitted a detailed characterization of the inhibition of hGH bioactivity by rhGHBP. The hormonal specificity confirms earlier radioligand binding studies, except that we found that the 20 kDa hGH variant interacts with the rhGHBP.

Journal of Endocrinology (1994) 140, 445–453