Search Results

You are looking at 1 - 10 of 22 items for

  • Author: J. Wright x
Clear All Modify Search
Full access

R. E. J. DYBALL and R. J. WRIGHT

A. R. C. Institute of Animal Physiology, Babraham, Cambridge, CB2 4AT

(Received 12 April 1977)

Both electrical stimulation with steel microelectrodes and injection of iron salts into the preoptic area lead to an increased concentration of luteinizing hormone (LH) in the plasma and ovulation (Everett & Radford, 1961; Dyer & Burnet, 1976).

Initially, iron salts were thought to excite nerve cells but Fe2+ and Fe3+ ions, like most cations, when applied to nerve cells by micro-iontophoresis, inhibit firing (Dyer & Burnet, 1976). Dyer & Burnet (1976) proposed a number of alternative explanations for the electrochemical stimulation of ovulation. They suggested that ferrous or ferric ions might kill or damage some neurones and the resulting cell disruption might lead in turn to the liberation of a sufficient quantity of luteinizing hormone releasing hormone (LH-RH) into the hypophysial portal vessels to cause a surge of LH. Alternatively, ovulation might be stimulated by

Full access

P. J. Wright and I. J. Clarke

ABSTRACT

The nature of the gonadotrophin-releasing hormone (GnRH) stimulus of the pituitary necessary for the oestrogen-induced plasma LH surge was studied in ovariectomized ewes. The sheep were treated with oestradiol benzoate (50 μg i.m.) at 0 h, and the hypothalamic contribution to the LH surge was blocked by pentobarbitone anaesthesia over the time during which the surge was expected (11–31 h). Pituitary responsiveness to exogenous GnRH (100 ng) administered i.v. in a pulsatile mode (once per hour or once per 20 min) over the period 15–30 h was assessed from plasma concentrations of LH. Neither of the GnRH treatments induced patterns of LH secretion similar to those seen in conscious ovariectomized ewes given oestrogen only. Plasma LH secretion in response to hourly GnRH pulses was less (P<0·01) than that associated with oestrogen-induced plasma LH surges in conscious control ewes. With pulses of GnRH administered every 20 min the amount of LH released was greater (P<0·05) than that in oestrogen-treated conscious control ewes. In contrast to the single surge induced by oestradiol in conscious ewes, GnRH pulses given every 20 min elicited phasic patterns of LH secretion consisting of two or three distinct surges. The failure of GnRH treatment to elicit an LH surge similar to an oestrogen-induced surge could reflect inappropriate GnRH treatment regimens, and/or inadequate priming of the pituitary with GnRH after induction of anaesthesia but before GnRH treatment.

J. Endocr. (1988) 116, 143–148

Full access

M. PEAKER, J. G. PHILLIPS and A. WRIGHT

SUMMARY

When injected intravenously, 20 i.u. ovine prolactin significantly enhanced the output of fluid from the minimally stimulated nasal salt-gland of ducks within 5 min. This effect persisted for a further 5 min. In ducks which were still producing nasal fluid 25 min. after prolactin administration, a second enhancement of secretion was observed which could be related to an indirect effect induced by a rise in the blood glucose concentration. The initial, rapid enhancement of secretion could not be attributed to changes in blood composition and it seems possible that prolactin may have a direct effect on the avian salt-gland.

Full access

M. PEAKER, STEPHANIE J. PEAKER, J. G. PHILLIPS and A. WRIGHT

SUMMARY

Ducks given corticotrophin (ACTH) i.m. for 5 days secreted significantly more nasal fluid in response to an i.v. injection of 0·5 m-NaCl. However, blood glucose and plasma potassium concentrations also increased in the birds given ACTH and when these changes in blood composition were produced by injecting glucose or KC1, an effect similar to that of ACTH was obtained, suggesting that glucocorticoids influence the salt gland indirectly rather than, or as well as, directly. The concentrations of Na+ and K+ in the nasal fluid were decreased by ACTH, an effect not mimicked by glucose or KC1, and this might suggest some direct influence on water movements in the salt gland. ACTH increased nasal secretion in response to a minimal stimulatory salt load approximately 15 min after i.v. injection and this increase coincided with a marked rise in blood glucose concentration.

Full access

J. G. ALLEN, G. H. THOMAS and A. A. WRIGHT

SUMMARY

The oxosteroid metabolites of the pregnant rabbit were identified by gas chromatography using a combination of chromatographic runs involving examination of the free and acetylated material on QF-1, the alcohols on SE-30 and the trimethylsilyl ethers on neopentyl glycol adipate (NGA). The oxidized material was run on QF-1 and NGA. The ketonic fraction consisted mainly of pregnanes, some of which were 20-oxosteroids (3α-hydroxy-5β-pregnan-20-one, 3α,6α-dihydroxy-5α-pregnan-20-one and its 5β-epimer, and 3α-hydroxy-5β-pregnane-11,20-dione), and two of which were 20α-ol-3-ones (20α-hydroxypregn-4-en-3-one and 20α-hydroxy-5β-pregnan-3-one). The detection of the latter two compounds directs attention to the catabolic pathway for pregnanediol which involves initially reduction of the 20-ketone.

Full access

A. WRIGHT, J. G. PHILLIPS and D. P. HUANG

SUMMARY

Domestic ducks were adenohypophysectomized and 2–3 weeks later were loaded with hypertonic saline. Normal intact ducks and sham-operated ducks were similarly treated. For 2 hr. nasal gland secretion was almost completely inhibited (0·20 g.) in the adenohypophysectomized ducks and was significantly reduced (4·93 g.) in the sham-operated ducks compared with the normal intact controls (14·74 g.).

When the renal response of the adenohypophysectomized ducks was compared with that of the normal intact controls no significant difference was found as far as volume of urine and concentration of Na+ and K+ were concerned. When compared with sham-operated controls, however, these values were significantly lower in adenohypophysectomized ducks.

The adrenal weight was not significantly reduced in the adenohypophysectomized ducks, but the weights of thyroid, nasal gland and testis decreased significantly. Histological examination of the adrenal glands of the adenohypophysectomized ducks showed that the central regions were atrophic while the peripheral regions remained normal. Nasal glands, thyroid glands and testes were also examined.

It is concluded that the adenohypophysis plays a major part in regulating extrarenal excretion.

Full access

A. WRIGHT, I. CHESTER JONES and J. G. PHILLIPS

SUMMARY

The histology of freshly fixed adrenal glands of Ornithorhynchus and of Tachyglossus has been investigated.

In the adrenals of both species the bulk of the chromaffin tissue was found to occur at one pole, the lower or caudal part of the gland. The adrenal cortex of Ornithorhynchus has a complicated histological appearance and comprises three main types of tissues, designated groups I-III. The major portion of the cortex was made up of groups II and III tissues which were in contiguous patches associated with blood vessels. Group I tissue was confined, for the most part, to a layer of cells lying against the chromaffin tissue. Group III tissue consisted of big cells with large nuclei which frequently contained prominent globules or vacuoles. It is possible that group III represents the secreting part of the cortex and group II the formative layer.

In Tachyglossus, the cortex had a more homogeneous appearance and was more akin to that of reptiles. There was, however, some gradation of cell types. The peripheral cells had plentiful cytoplasm with faintly basophilic nuclei, while centripetally the cells were closely packed and the nuclei densely stained.

Full access

J. C. DRUMMOND, R. L. NOBLE and MARGARET D. WRIGHT

Although it is now established that deprivation of vitamin E may lead to disturbances of structure and function of many tissues other than those primarily concerned in the reproductive cycle, it is not surprising, when the striking nature of the testicular degeneration and the curious character of the typical resorption in the female are borne in mind, that there has been a tendency to concentrate attention on the question whether the vitamin plays an essential part in the reproductive cycle.

The most direct approach has been made by investigating whether the vitamin itself exerts a gonadotrophic action. Up to the present the evidence has been inconclusive. The most striking claim is that of Szarka [1929], who stated that oral or parenteral administration of vitamin E concentrates produces oestrus in immature female rats. Later, Verzár [1931] recorded that injection of similar materials produced hypertrophy of the uterus in similar animals, but

Full access

R. J. FRANKEL, J. S. JENKINS, J. J. WRIGHT and M. U. A. KHAN

SUMMARY

The lateral hypothalamus, and various sites within the limbic system and frontal lobe of the rhesus monkey brain were electrically stimulated using chronically implanted electrodes. A considerable increase in plasma aldosterone levels was observed after stimulation of the lateral hypothalamic area, certain localized sites in the cingulate area, and lower medial parts of the frontal lobe. Inactive sites included most of the amygdala, hippocampus, and basal ganglia, together with other areas within the frontal lobe and cingulate gyrus. Stimulation of all active areas was followed by an increase in plasma renin activity. Plasma cortisol also increased considerably after hypothalamic stimulation but in the case of extra-hypothalamic sites the cortisol response was much less.

Full access

J. S. JENKINS, R. J. FRANKEL, J. J. WRIGHT and M. U. A. KHAN

SUMMARY

The increase in aldosterone and plasma renin activity (PRA) observed after stimulation of extrahypothalamic sites within the brain of the rhesus monkey was prevented by the prior administration of the β-adrenergic blocking agent propranolol. α-Adrenergic blockade by phentolamine had no inhibiting effect. Propranolol only partially reduced the response of aldosterone to lateral hypothalamic stimulation in spite of inhibition of PRA; a partial reduction in aldosterone was also obtained from this site after dexamethasone treatment without any effect on PRA. It was concluded that the increase in aldosterone observed after extra-hypothalamic stimulation was mediated mainly through the renin-angiotensin mechanism whereas in the case of the hypothalamus, release of ACTH was also a contributory factor.