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M Shimizu, A Hara and WW Dickhoff

Salmon plasma contains at least three IGF-binding proteins (IGFBPs) with molecular masses of 41, 28 and 22 kDa. The 41 kDa IGFBP is similar to mammalian IGFBP-3 in size, type of glycosylation and physiological responses. In this study, we developed an RIA for the 41 kDa IGFBP. The 41 kDa IGFBP purified from serum was used for antibody production and as an assay standard. Binding of three different preparations of tracer were examined: (125)I-41 kDa IGFBP, (125)I-41 kDa IGFBP cross-linked with IGF-I and 41 kDa IGFBP cross-linked with (125)I-IGF-I (41 kDa IGFBP/(125)I-IGF-I). Only binding of 41 kDa IGFBP/(125)I-IGF-I was not affected by added IGFs, and therefore it was chosen for the tracer in the RIA. Plasma 41 kDa IGFBP levels measured by RIA were increased by GH treatment (178.9+/-4.9 ng/ml) and decreased after fasting (95.0+/-7.0 ng/ml). The molarities of plasma 41 kDa IGFBP and total IGF-I were comparable, and they were positively correlated, suggesting that salmon 41 kDa IGFBP is a main carrier of circulating IGF-I in salmon, as is mammalian IGFBP-3 in mammals. During the parr-smolt transformation (smoltification) of coho salmon, plasma 41 kDa IGFBP levels showed a transient peak (182.5+/-10.3 ng/ml) in March and stayed relatively constant thereafter, whereas IGF-I showed peak levels in March and April. Differences in the molar ratio between 41 kDa IGFBP and IGF-I possibly influence availability of IGF-I in the circulation during smoltification.

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Department of Pathophysiology, Atomic Disease Institute, Nagasaki University School of Medicine, Nagasaki, Japan

(Received 17 February 1975)

The mechanism underlying the depletion of ascorbic acid content of steroid-producing tissues in response to trophic hormones is poorly understood. Previous work (Koba, Kawao & Yamashita, 1971) has shown that, in the dog, the discharge of ascorbic acid as well as 17-oxosteroids into spermatic venous blood by testicular tissue stimulated with human chorionic gonadotrophin (HCG) can be suppressed by the prior administration of methylenedianiline, an amphenone analogue capable of inhibiting testicular steroidogenesis (Yamashita, 1967). Since oestrogens have been shown to be effective inhibitors of the glucose-6-phosphate dehydrogenase necessary for corticosteroid synthesis in the rat adrenal (McKerns, Coulomb, Kaleita & De Renzo, 1958), we have studied male dogs pretreated with oestradiol-17β.

Eight adult male mongrel dogs weighing 9·6–15·1 kg were used. Four animals were given 20 μg oestradiol-17β (dissolved in 0·2 ml sesame oil)/

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Department of Pathophysiology, Atomic Disease Institute, Nagasaki University School of Medicine, Nagasaki, Japan

(Received 16 December 1974)

We have reported the inhibitory effect of methylenedianiline, a diaminodiphenyl derivative related to amphenone B, on the testicular 17-oxosteroid secretion stimulated by human chorionic gonadotrophin (HCG) (Yamashita, 1967). Unlike amphenone B (Rosenfeld & Bascom, 1956) and methylenedianiline (Tullner, 1960), Metopirone has been shown to be a relatively selective inhibitor of 11β-hydroxylase in the adrenal cortex (Liddle, Island, Lance & Harris, 1958). However, since it also is an amphenone analogue (Chart, Sheppard, Allen, Bencze & Gaunt, 1958), the present study was undertaken to see whether it exerts an amphenone-like effect on androgen synthesis and release by the testis.

Spermatic venous blood was collected from 15 mongrel dogs, weighing between 7·9 and 13·1 kg, by the method described previously (Yamashita, 1966). In each dog the left spermatic vein was exposed by the lumbar route under

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H Kadokawa, M Matsui, K Hayashi, N Matsunaga, C Kawashima, T Shimizu, K Kida and A Miyamoto

This study was conducted to estimate the effects of kisspeptin-10 on blood concentrations of LH and GH in prepubertal dairy heifers. Heifers received a single injection of 1 mg kisspeptin-10 (n=5) or saline (n=5) intravenously, and serial blood samples were collected at 15-min intervals to analyze the response curves of both LH and GH after injection. Peak-shaped responses were observed for concentrations of LH and GH, and the peaks were observed at 27±3 and 75±9 min, respectively, after injection, only in heifers injected with kisspeptin-10. These data suggest various possible important links among kisspeptin, the reproductive axis, and also the somatotropic axis in prepubertal Holstein heifers.

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A L Pierce, M Shimizu, L Felli, P Swanson and W W Dickhoff

IGF-binding proteins (IGFBPs) modulate the effects of the IGFs, major stimulators of vertebrate growth and development. In mammals, IGFBP-1 inhibits the actions of IGF-I. Rapid increases in circulating IGFBP-1 occur during catabolic states. Insulin and glucocorticoids are the primary regulators of circulating IGFBP-1 in mammals. Insulin inhibits and glucocorticoids stimulate hepatocyte IGFBP-1 gene expression and production. A 22 kDa IGFBP in salmon blood also increases during catabolic states and has recently been identified as an IGFBP-1 homolog. We examined the hormonal regulation of salmon IGFBP-1 mRNA levels and protein secretion in primary cultured salmon hepatocytes. The glucocorticoid agonist dexamethasone progressively increased hepatocyte IGFBP-1 mRNA levels (eightfold) and medium IGFBP-1 immunoreactivity over concentrations comparable with stressed circulating cortisol levels (10−9–10−6 M). GH progressively reduced IGFBP-1 mRNA levels (0.3-fold) and medium IGFBP-1 immunoreactivity over physiological concentrations (5 × 10−11–5 × 10−9 M). Unexpectedly, insulin slightly increased hepatocyte IGFBP-1 mRNA (1.4-fold) and did not change medium IGFBP-1 immunoreactivity over physiological concentrations and above (10−9–10−6 M). Triiodothyronine had no effect on hepatocyte IGFBP-1 mRNA, whereas glucagon increased IGFBP-1 mRNA (2.2-fold) at supraphysiological concentrations (10−6 M). This study suggests that the major inhibitory role of insulin in the regulation of liver IGFBP-1 production in mammals is not found in salmon. However, regulation of salmon liver IGFBP-1 production by other metabolic hormones is similar to what is found in mammals.

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T Akamizu, T Murayama, S Teramukai, K Miura, I Bando, T Irako, H Iwakura, H Ariyasu, H Hosoda, H Tada, A Matsuyama, S Kojima, T Wada, Y Wakatsuki, K Matsubayashi, T Kawakita, A Shimizu, M Fukushima, M Yokode and K Kangawa

Aging is associated with a decrease in growth hormone (GH) secretion, appetite and energy intake. As ghrelin stimulates both GH secretion and appetite, reductions in ghrelin levels may be involved in the reductions in GH secretion and appetite observed in the elderly. However, only preliminary studies have been performed on the role of ghrelin in elderly subjects. In this study, we sought to clarify the physiologic implications of the age-related alterations in ghrelin secretion by determining plasma ghrelin levels and other clinical parameters in healthy elderly subjects. Subjects were ≥ 65 years old, corresponding to the SENIEUR protocol, had not had a resection of the upper gastrointestinal tract and had not been treated with hormones. One hundred and five volunteers (49 men and 56 women) were admitted to this study (73.4 ± 6.3 years old). Plasma levels of acylated ghrelin in elderly female subjects positively correlated with serum IGF-I levels and bowel movement frequency and negatively with systolic blood pressure. In elderly men, desacyl ghrelin levels correlated only weakly with bowel movement frequency. These findings suggest that the plasma levels of the acylated form of ghrelin may influence the age-related alterations in GH/IGF-I regulation, blood pressure and bowel motility. These observational associations warrant further experimental studies to clarify the physiologic significance of these effects.