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SUMMARY
Serum samples from rabbits, sheep and rats containing immunoreactive luteinizing hormone releasing hormone (LH-RH) have been extracted and fractionated by ion exchange chromatography on carboxymethylcellulose followed by radioimmunoassay of the fractions. Control experiments showed that the extraction and chromatographic procedures did not alter the mobility of synthetic LH-RH. Four immunoreactive components of circulating LH-RH in blood samples from various species at various times were identified on CM-cellulose columns. One of these had a mobility identical with that of synthetic LH-RH; of the others, two were eluted before and one after synthetic LH-RH. The nature, site of formation and possible significance of the extra components are discussed.
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SUMMARY
The clearance of synthetic luteinizing hormone releasing hormone (LH-RH) after intravenous injection has been investigated in man. Thirteen tests were performed in ten subjects, four of whom were normal, the other six had proven disease of the hypothalamo-pituitary region. The rate of disappearance of LH-RH from the circulation could be represented as a double exponential with half-times of the two components of 5·3 and 27·4 min respectively. The initial volume of distribution was 11·1 ± 1·6 (s.d.) 1 and the metabolic clearance rate 1480 ± 170 (s.d.) 1/day. There was no difference in any of these parameters between normal and abnormal subjects. Between 0·75 and 2·8% of the injected dose was excreted in the urine within 8 h, of which 48% was excreted in the first hour. The daily production rates of LH-RH were calculated from the urinary excretion rates; these gave higher results than production rates calculated from the blood metabolic clearance rate. Possible reasons for this are discussed.
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SUMMARY
Luteinizing hormone and LH-RH-like immunoreactivity were measured in the jugular venous plasma of Clun Forest ewes at various stages of the oestrous cycle.
Blood samples were collected through jugular venous cannulae every 2 h for at least 20 days from three ewes during the breeding season. The ewes were checked twice daily for oestrus using a vasectomized ram. Plasma LH peaks of apparent height 112–192 ng NIH-LH-S17 equivalents/ml were detected at oestrus with basal levels of 2–15 ng/ml during most of the remainder of the 17-day oestrous cycle. Peaks of LH-RH-like immunoreactivity occurred at various times of the cycle. The apparent maximal level of these peaks was 220 pg/ml compared with basal levels of < 10 pg/ml. Further ewes (two for each group) were sampled at 4 min intervals for 12 h, (1) from onset of oestrus, (2) 36–48 h after onset of oestrus or (3) on day 10 of the oestrous cycle. In the ewes sampled at oestrus, peaks of LH-RH-like immunoreactivity were detected before, during and after the preovulatory LH peak. Those detected after the LH peak were unassociated with any further increases in the plasma LH level. In the ewes sampled 36–48 h after onset of oestrus and on day 10 of the cycle, several peaks of LH-RH-like immunoreactivity unassociated with any increases in the LH level were detected. These peaks, and those detected at oestrus, had durations of only one or two samples, and in some cases reached levels of several ng/ml compared with basal levels of < 10 pg/ml. The significance of these results is discussed.
Search for other papers by M. D. Holland in
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ABSTRACT
A quantitative, repeatable, heterologous radioimmunoassay (RIA) for insulin-like growth factor-I (IGF-I) was developed for bovine serum. Untreated serum could not be assayed due to interference by IGF-I-binding protein. Serum acidified to pH 3·6 in glycine–HCl (0·1 mol/l) for 24 h at 37 °C and neutralized with NaOH produced inhibition curves non-parallel to the [Thr59]-IGF-I standard. Neutralization by 40-fold dilution of acidified serum samples with assay buffer produced inhibition curves nearly parallel to the IGF-I standard. Complete parallelism was achieved by utilizing preprecipitated normal rabbit serum–sheep anti-rabbit γ-globulin to separate antibody-bound 125I-labelled IGF-I from free 125I-labelled IGF-I. Recovery of IGF-I (1·3–52·3 fmol) added to serum was quantitative. The sensitivity of the RIA (n = 6) was 8·25 ± 0·17 (s.e.m.) fmol. Intra- and interassay coefficients of variation were 3·03 and 4·95% respectively. Serum IGF-I levels measured in beef calves at weaning were positively correlated with weaning weight, total weight gain from birth to weaning and average daily weight gain. In conclusion, a heterologous RIA for IGF-I in beef serum which is sensitive, accurate, precise and repeatable has been developed.
J. Endocr. (1988) 119, 281–285
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Search for other papers by S. L. JEFFCOATE in
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The occurrence of a peak of luteinizing hormone (LH) in the peripheral blood of the sheep within the first 16 h of oestrus is well established (Geschwind & Dewey, 1968; Niswender, Roche, Foster & Midgley, 1968; Goding, Catt, Brown, Kaltenbach, Cumming & Mole, 1969). Changes in the LH releasing hormone (LH-RH) content of the hypothalamus have been correlated with the occurrence of the plasma LH peak and the accompanying decline in pituitary LH content (Crighton, Hartley & Lamming, 1973). Using a radioimmunoassay for LH-RH, Kerdelhué & Jutisz (1972) detected increases in plasma LH-RH content in one ewe 2 days before the LH peak and again from 1 h before the start of the LH peak to 8 h after its end. The present report describes the simultaneous determination of LH and LH-RH in samples taken at frequent intervals from onset of oestrus in the sheep.
Serial blood samples (2·5 ml)
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SUMMARY
Luteinizing hormone releasing hormone (LH-RH) was detected in hypothalamic extracts of rats, rabbits and chickens using a radioimmunoassay for synthetic LH-RH decapeptide. The mobilities of the immunologically active fraction and of synthetic LH-RH were the same in various chromatographic systems (gel filtration on Sephadex, thin-layer chromatography on silica gel and ion-exchange chromatography on carboxymethylcellulose) suggesting that mammalian, avian and synthetic LH-RH's are closely related.
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*Department of Surgery, University of Dundee, Dundee, DD1 4HN and †Department of Chemical Pathology, St Thomas's Hospital, London, SE1 7EH
(Received 23 August 1974)
Short-term inhibition of luteinizing hormone releasing hormone (LH-RH) in vivo can be conveniently studied by injection of antisera (Fraser & Gunn, 1973), and in the ovariectomized rat this was found to reduce both luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels when measured 7 and 24 h after injection (Koch, Chobsieng, Zor, Fridkin & Lindner, 1973). Long-term inhibition of LH-RH cannot be satisfactorily achieved by injection of antisera but is induced by active immunization. In a previous study we have shown in the male rat that this results in low levels of LH and FSH in serum and pituitary, suggesting that LH-RH is required for synthesis as well as release of both LH and FSH (Fraser, Gunn, Jeffcoate & Holland, 1974). In this study, the work
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ABSTRACT
Corticotrophin-releasing factor (CRF) bioactivity has been described in the extra-hypothalamic brain, but its relationship to hypothalamic CRF has remained questionable. Of the seven regions of the mouse brain examined, highest concentrations of CRF-like immunoreactivity (CRF-LI) and bioassayable CRF activity were present in the median eminence and hypothalamus. However, substantial CRF-LI and bioassayable CRF activity were also seen in brain extracts from the amygdala, thalamus, frontal cortex, pons medulla and cerebellum. Bioactivity was largely neutralized by prior incubation with heat-inactivated antiserum to ovine CRF. These findings, in conjunction with previous immunocytochemical evidence, strongly suggest that a substance closely resembling hypothalamic CRF is present in the extrahypothalamic brain of the mouse.
J. Endocr. (1986) 111, 143–149
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Search for other papers by DIANE T. HOLLAND in
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SUMMARY
The pineal indole 5-methoxytryptophol (ML) has been shown to have an antigonadal activity when administered to experimental animals, but data on its normal pattern of secretion have been lacking. Using a new gas chromatography–mass spectrometry assay, the concentration of ML at various phases of the human menstrual cycle has been studied. Daily samples were obtained throughout the month from five women with a normal cycle and two women taking an oral contraceptive. In women with a normal cycle levels of ML were found to be significantly lower in the last third of their cycle; this change was not seen in women taking an oral contraceptive who had low levels throughout the month. The changes in concentration of ML did not correlate with the changes in concentration of gonadotrophins.
