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J. N. BALL and D. M. ENSOR

The pituitary of the cyprinodont fish Poecilia secretes a hormone that is essential for tolerance of freshwater. Intact fish are euryhaline, but when hypophysectomized cannot tolerate fresh water, though living indefinitely in sea water or dilute sea water. In a typical experiment, ten hypophysectomized P. latipinna, transferred from dilute sea water (12 parts/1000) to fresh water at 25°, displayed severe distress symptoms within 8–46 hr. (mean, 22 hr.). When distressed in fresh water, hypophysectomized fish die in a few hours, but recover if returned immediately to dilute sea water (Ball, unpublished).

The pituitary factor essential for freshwater life is probably not a neurohypophysial hormone, since it is secreted by ectopic pituitary transplants in P. formosa (Ball, Olivereau, Slicher & Kallman, 1965), in which the neurohypophysis is involuted and virtually devoid of histologically detectable neurosecretion (Olivereau & Ball, unpublished observations). Histological studies of the adenohypophysis of P. latipinna and of the

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K Kauter, M Ball, P Kearney, R Tellam and McFarlane JR

Leptin, a recently discovered hormone secreted mainly from adipose tissue, was first described as a regulator of adiposity, food intake and energy metabolism. It is now apparent that leptin physiology is much more complex and is likely to play an important role in many other systems including reproduction, haematopoiesis and immunity. Leptin levels have been shown to be well correlated with body fat in both humans and rodents, with administration of exogenous leptin to rats and mice resulting in loss of body fat. Leptin is, therefore, likely to be an important humoral signal to the central nervous system on body composition and regulation of food consumption. Due to the limited cross-reactivity of leptin from other species in the current assays for leptin, physiological research on leptin has, to a large extent, been restricted to rodents and humans. The aim of this study was to develop a leptin immunoassay suitable for use with sheep, enabling the investigation of the basic physiology of leptin in an animal larger than rats or mice, thus allowing repeated blood sampling. Using this assay we investigated the short-term effects of insulin, adrenaline and glucagon (all modulators of blood glucose) on plasma leptin levels. Antiserum to bovine recombinant leptin (brLeptin) raised in chickens was used to develop a competitive ELISA. Using brLeptin as standard, the assay has a sensitivity of 0. 5 ng/ml with inter- and intra-assay variation of 15% and 7% respectively. The cross-reactivity of human recombinant leptin was 36.5%, while mouse leptin showed no cross-reactivity. Plasma samples from ewes, male castrate animals and rams (n=4-5) diluted in parallel to the standard with mean leptin concentrations of 6.0+/-2. 9, 3.3+/-0.4 and 3.1+/-1.3 ng/ml respectively. Leptin levels in rams were significantly lower than in ewes. The non-significant difference in leptin levels between rams and male castrate animals suggests that testosterone may not be responsible for the lower levels of leptin. Four groups of 3-4 ewes were given intravenous insulin (1 iu/kg), adrenaline (65 microg/kg), glucagon (24 iu/kg) or saline. Blood samples were taken at 1, 3, 5, 10, 20, 30, 60, 90 and 120 min after injection. As expected, glucose levels declined within 10 min of the insulin injection and rose after 3 min following both adrenaline and glucagon injections. Leptin levels, however, remained relatively unchanged for the 2 h following the treatments. Finally, a bolus intravenous dose of glucose (240 mg/kg) was given and sequential blood samples taken. Despite plasma glucose levels rising to over 200 mg/dl, leptin levels did not significantly change over the three hours following treatment. These data indicate that plasma leptin levels in sheep, in contrast to rodents, are not responsive to short-term changes in blood glucose or insulin, as has been shown in humans.

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K. M. Henderson, P. Franchimont, M. J. Lecomte-Yerna, N. Hudson and K. Ball

ABSTRACT

Four Romney ewes were actively immunized with a partially purified preparation of inhibin derived from bovine follicular fluid and their ovulation rates in four successive oestrous cycles were compared with those of four ewes receiving adjuvant alone. The ovulation rates of the ewes immunized with the inhibin preparation were significantly higher than those of the control ewes (2·06 ± 0·16 (s.e.m.) vs 1·31±0·06 ovulations/ewe, n= 4). Plasma concentrations of FSH and LH, measured in blood samples taken three times a week for 11 weeks, during which time each ewe was immunized three times, were not significantly different between the two treatment groups. These results suggest that active immunization with inhibinenriched follicular fluid may be a potential means of increasing fecundity in sheep.

J. Endocr. (1984) 102, 305–309

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V.K.K. Chatterjee, J.A. Ball, C. Proby, J.M. Burrin and S.R. Bloom

ABSTRACT

In five healthy normal male volunteers, pretreatment with the cholinergic muscarinic antagonist pirenzepine (30 mg i.v.) almost abolished the growth hormone (GH) response to a maximal dose (120 μg i.v.) of growth hormone-releasing hormone (GHRH) (GH response at 40 min 5.6 ± 1.3 mU/l with GHRH and pirenzepine vs 40.8 ± 5.3 mU/l with GHRH alone, P <0.02). Concomitant i.v. infusion of galanin (40 pmol/kg/min) with pirenzepine not only restored but significantly potentiated the GH response to GHRH (GH at 40 min 72.2 ± 10.5 mU/l, P <0.001 vs GHRH and pirenzepine, P <0.02 vs GHRH alone). Previous studies have proposed that cholinergic pathways control GH release via samatostatin and this study suggests that galanin may act by modulating hypothalamic somatostatinergic tone either directly or, possibly, by facilitating cholinergic neurotransmission.

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J. M. C. Connell, C. J. Kenyon, S. G. Ball, D. L. Davies and R. Fraser

ABSTRACT

The effect of dopamine (1 μg/kg per min) on corticosteroid response to ACTH (0·1, 1 and 10 ng/kg per min) was compared with that of a placebo in sodium-replete (150 mmol/day) and -deplete (10 mmol/day) normal man. Dopamine had no effect on aldosterone, cortisol or corticosterone responses in either dietary phase, but increased deoxycorticosterone (897·0 ± 126·4 (s.e.m.) vs 590·0 ±84·3 pmol/l, normal Na+; 1264·2 ±84·3 vs 764·5 ±84·3 pmol/l, low Na+) and deoxycortisol (6·033 ± 0·583 vs 5·048±0·680 nmol/l, normal Na+; 5·112 ± 0·600 vs 4·130± 0·367 nmol/l, low Na+) levels during ACTH administration (all P <0·01). Deoxycorticosterone and corticosterone responses to ACTH were greater during sodium depletion than repletion (both P <0·01).

Dopamine therefore increased 11-deoxycorticosteroid concentrations during ACTH-stimulated steroidogenesis. This may reflect action of dopamine to increase extra-adrenal formation of 11-deoxycorticosteroids.

J. Endocr. (1986) 109, 339–344

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K. P. McNatty, N. Hudson, M. Gibb, K. Ball, J. Fannin, L. Kieboom and D. C. Thurley

ABSTRACT

The aim of the present study was to establish whether cyclic ovarian activity could be induced and then maintained in anoestrous Romney ewes by the long-term administration of regular intravenous pulses of LH (10 μg ovine LH i.v. once every 1 or 2 h for 29–91 days). The LH pulse regimen was designed to generate plasma profiles of LH that were comparable to those experienced during the luteal and follicular phases of the oestrous cycle.

The results showed that the LH treatments were capable of inducing cyclic ovarian activity, as assessed from the concentrations of progesterone in plasma, but that the treatments were inadequate for sustaining cyclic activity beyond two consecutive progestational phases. After 35–56 days of treatment, the plasma concentrations of FSH declined significantly (P <0·05) relative to those in the untreated animals. These data suggest that FSH supplementation as well as LH might be required for the long-term maintenance of cyclic ovarian activity in seasonally anoestrous ewes.

J. Endocr. (1984) 100, 67–73

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J. M. C. Connell, G. Tonolo, D. L. Davies, J. Finlayson, S. G. Ball, G. Inglis and R. Fraser

ABSTRACT

Infusion of dopamine is reported to reduce the response of aldosterone to infused angiotensin II in sodium-deplete but not sodium-replete man. Six normal male subjects were infused with angiotensin II in graded doses (2, 4 and 8 ng/kg per min) with or without dopamine (1·0 μg/kg per min) during both dietary sodium repletion and depletion. The responses of both aldosterone and 18-hydroxycorticosterone to infusion of angiotensin II appeared to be reduced by dopamine in sodium-deplete, but not sodium-replete, subjects. However, when the relationships between plasma concentrations of angiotensin II and corticosteroid were examined it was evident that plasma concentrations of angiotensin II were lower when dopamine was infused concurrently with the peptide (P<0·05).

In a second study, six sodium-deplete males were infused with angiotensin II at a constant rate (6 ng/kg per min) while dopamine (or placebo) was given in graded doses (0·5,1 and 5 μg/kg per min). Renal plasma flow was estimated from total body clearance of para-aminohippuric acid. Overall, angiotensin II concentrations were lower during dopamine infusion compared with those during infusion of placebo (63·2 ± 9·7 (s.e.m.) vs 92·3±6·4 pmol/l; P<0·01) and this was associated with a 40% increase in effective renal plasma flow (627 ± 68 vs 451 ± 15 ml/min; P < 0·05); there again appeared to be a reduced aldosterone response during combined angiotensin II/dopamine infusion compared with that during infusion of angiotensin II alone (1003 ± 404 vs 1225± 146 pmol/l; 0·05<P<0·1).

Dopamine appeared to increase the metabolic clearance of infused angiotensin II, possibly by altering blood flow through vascular beds, such as renal, which degrade the peptide. This may partly explain the effects of dopamine on the response of the adrenal to infusion of angiotensin II in sodium-deplete man; the physiological role of dopamine in the regulation of corticosteroidogenesis remains speculative.

J. Endocr. (1987) 113, 139–146

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J. N. BALL, I. CHESTER JONES, M. E. FORSTER, G. HARGREAVES, E. F. HAWKINS and K. P. MILNE

SUMMARY

The competitive protein-binding radioassay (CPB method) of Murphy (1967) has been adapted to determine total cortisol levels in the plasma of the eel, Anguilla anguilla L. Validation of the method for this species depended in part on the development of a chromatographic—fluorimetric technique for eel cortisol, following classical procedures and using radioactive tracers; by this means, the specificity of the CPB method for cortisol in eel plasma was established. Accuracy, precision and sensitivity of the CPB method were also investigated and were shown to be satisfactory.

Plasma total cortisol levels were determined in eels during osmotic adjustments after transfers from fresh water (FW) to sea-water (SW) and vice versa, and from FW to distilled water. Plasma osmotic pressure and/or sodium levels were monitored simultaneously, to follow the progress of osmotic regulation. In only one of the transfer situations did the plasma cortisol level change significantly, showing a marked transitory increase during the first few days after transfer from FW to SW, corresponding to the development and correction of an 'osmotic crisis'. Plasma cortisol levels were the same in eels adapted for long periods to FW and to SW. Plasma cortisol fell to extremely low levels after hypophysectomy.

These results are discussed in the light of the literature on hormonal control of osmoregulatory mechanisms in the eel, with particular emphasis on the role of adrenocorticosteroids in ionic regulation of animals in SW.