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ABSTRACT

Small non-atretic follicles (1·5–250 mg) were collected from four distinct areas of the ovary of the laying hen. These were as follows: (1) the stalks of the two largest preovulatory follicles; (2) the stalks of the third largest preovulatory follicle; (3) the stalks of the fourth and fifth largest preovulatory follicle and (4) zona parenchymatosa.

There was an increase in the proportion of small follicles in the size range 1·5–10 mg collected from the stalks of the large yellow yolky preovulatory follicles approaching ovulation, with a corresponding decrease in the number of small follicles in the size group 10–250 mg. In addition, the ornithine decarboxylase activity in follicles collected from regions 1 and 2 was significantly greater than that in small follicles collected from region 4.

Since the level of ornithine decarboxylase activity is critically dependent on the degree of hormonal stimulation and growth rate of the tissue, it is suggested, on the basis of the differences in their ornithine decarboxylase activity, that small follicles located on the stalks of the large yolky preovulatory follicles are stimulated by trophic hormones and growth factors to a greater degree than similarly sized follicles located elsewhere in the ovary. It is proposed that this increased stimulation may increase the chances of these small follicles being recruited into the hierarchy.

J. Endocr. (1987) 112, 183–187

ABSTRACT

The object of this study was to examine changes in the activity of granulosa 3β-hydroxy-Δ⁵-steroid dehydrogenase during the ovulatory cycle of the domestic fowl. The enzyme activity in granulosa tissue from the largest follicle increased significantly during the period 8–14 h before an expected ovulation. The increase in activity occurs before the preovulatory surge of LH and near the time of lights off. During the 4–8 h period before an ovulation, i.e. the time of maximal plasma LH concentrations, 3β-hydroxy-Δ⁵-steroid dehydrogenase activity decreased in granulosa tissue from the largest follicle. This observation is explained by proposing that the enzyme is inhibited by the large amounts of progesterone found in the tissue at this time.

The results indicate that important biochemical changes are taking place within granulosa tissue of the largest ovarian follicle before the preovulatory LH surge.

J. Endocr. (1985) 106, 269–273

ABSTRACT

The tritium release assay for measuring aromatase activity was adapted to measure oestrogen production in intact small ovarian follicles of the domestic fowl. The activity was measured in three types of follicle classified as normal, atretic or grossly atretic. Normal follicles were distinguished from atretic by the presence of small haemorrhages on the surface of the atretic follicles. Grossly atretic follicles were identified by their deformed shape.

The aromatase activity in normal and atretic follicles was related to follicular weight, the activity in atretic follicles being less than that in normal follicles. The aromatase activity in grossly atretic follicles was independent of follicular weight. The enzyme activity in this group of follicles was significantly less than that in either normal or atretic follicles. The significance of these results is discussed in relation to the induction of atresia within the small ovarian follicles of the domestic fowl.

J. Endocr. (1985) 105, 297–301

ABSTRACT

Fowl ovarian aromatase activity was measured by an assay based on the stereospecific elimination of tritium from [1,2-³H]testosterone. The production of tritiated water was shown to provide a valid estimate of aromatase activity under the conditions used.

The small yellow follicles and ovarian stroma contained 50% of the total ovarian aromatase activity. The activity in the thecal tissue from the rapidly growing follicles reached a maximum level in the fourth largest follicles (17% of the total ovarian activity) and thereafter declined to low levels in the largest follicle and first post-ovulatory follicle. No activity was detected in the granulosa tissue from the rapidly growing follicles.

It is proposed that the basal levels of plasma oestrogen in hens are maintained by production in the small yellow follicles and/or ovarian stroma. The variation in plasma oestrogen during the ovulatory cycle probably arises from secretion by the rapidly growing follicles.

J. Endocr. (1984) 100, 81–86

ABSTRACT

Fowl ovarian ornithine decarboxylase activity was measured at 20, 10 and 3 h before an expected ovulation in granulosa and thecal tissues from follicles at various stages of development. An increase in the enzyme activity between 10 and 3 h before an expected ovulation was assumed to be caused by preovulatory increase in plasma LH concentration.

The activity in granulosa tissue increased with increasing size of the follicle. In the largest (F1) follicle there was an 11-fold increase in granulosa ornithine decarboxylase specific activity between 10 and 3 h before ovulation. In the third (F3) and fifth (F5) largest follicles there was a 1·9- and 2-fold increase respectively.

The enzyme activity in thecal tissue from the follicular hierarchy decreased with increasing size of the follicle and the F3 thecal preparation was the only tissue to respond to the preovulatory LH surge. In contrast, ornithine decarboxylase activity in thecal tissue from small (< 5 mm) non-atretic follicles increased by two- to threefold after the preovulatory LH surge. The activity in atretic follicles of the same size was low and remained unchanged throughout the ovulatory cycle.

J. Endocr. (1986) 110, 211–216

The total and specific activity of 3β-hydroxy-Δ⁵-steroid dehydrogenase, isocitrate dehydrogenase (NADP⁺) and glucose-6-phosphate dehydrogenase were measured in ovarian follicles from the domestic fowl. The enzymes were assayed in the five largest yolk-filled follicles which were sampled twice during the ovulatory cycle, at 1 h and 16 h before an expected ovulation. The total and specific activity of granulosa enzymes increased throughout the hierarchy and reached a maximum in the largest follicle. The relative increase in 3β-hydroxy-Δ⁵-steroid dehydrogenase activity was greater than that of the other two enzymes examined. The total thecal 3β-hydroxy-Δ⁵-steroid dehydrogenase activity reached a maximum in the third and fourth largest follicles. Thereafter its activity decreased up to the time of ovulation. The activity of 3β-hydroxy-Δ⁵-steroid dehydrogenase and glucose-6-phosphate dehydrogenase in follicles collected 1 h before an ovulation were significantly less than the activity in corresponding follicles collected 16 h before an ovulation.

ABSTRACT

We evaluated the effects of [d-Ala²,Me,Phe⁴,Met(0)ol]-enkephalin (FK 33-824) and morphine, opioid receptor agonists, on concentrations of LH, cortisol and GH during the follicular phase in heifers. During three trials, oestrous cycles of Angus heifers were synchronized by two injections of prostaglandin F_2α (PGF_2α) resulting in 17 induced follicular phases over an 80-day period. Treatments were administered 24 h after the second injection of PGF_2α. Blood samples were collected at 15-min intervals from 3 h before until 5 h after i.v. administration of 2 ml physiological saline (trials 1, 2 and 3), 0·5 mg morphine/kg (trials 1 and 2) or 1·8 μg FK 33-824/kg (trials 1 and 2) or 6·7 μg FK 33-824/kg (trial 3). Administration of both doses of FK 33-824 and morphine inhibited episodic release of LH for approximately 60 min. The concentration of cortisol was increased (P<0·05) after both doses of FK 33-824, but was unaffected (P>0·5) by morphine or saline. The serum concentration of GH was increased (P<0·01) after both doses of FK 33-824 or morphine, but saline was without effect. These results provide evidence of an inhibitory effect of opioid receptor agonists on LH (FK 33-824 and morphine) and a stimulatory effect on cortisol (FK 33-824) and GH (FK 33-824 and morphine) during the follicular phase in heifers. Divergent effects of morphine and FK 33-824 on cortisol observed in this study provide evidence that opioid-induced changes in LH, GH and cortisol result from activation of different opioid receptors.

Journal of Endocrinology (1989) 121, 11–17

SUMMARY

Small doses of luteinizing hormone (LH) have been shown to exert a stimulating effect on the in vitro carbohydrate metabolism of the prepubertal rat ovary. In order to determine the specificity of the response, studies were undertaken comparing the effects caused by LH with those of other anterior pituitary hormones. Preparations of thyroid stimulating hormone (TSH) caused responses similar to those caused by LH, when added to the media in which prepubertal rat ovaries were incubated. A detailed study of the effects of TSH preparations (prepared by different procedures with known low levels of LH contamination) on lactic acid production, has been undertaken. All TSH preparations tested caused considerably greater stimulation of glycolysis than could be accounted for on the basis of their contamination with LH when the latter was appraised by the ovarian ascorbic acid depletion assay.

ABSTRACT

Changes in aromatase activity in the neuroendocrine tissues of captive male and female red grouse (Lagopus lagopus scoticus) were measured during a photoinduced breeding cycle. The gonads enlarged and subsequently regressed, as a consequence of the development of long-day refractoriness, within 84 days of transferring photoinsensitive birds from a non-stimulatory to a stimulatory daylength. The object of the study was to determine whether long-day refractoriness is related to an increase in aromatase activity in the neuroendocrine tissues which might result in a greater inhibitory action of locally produced oestrogens on the release of LH-releasing hormone.

Aromatase activity was measured and found to be present in the anterior pituitary gland, the anterior/ preoptic hypothalamus, the posterior hypothalamus and the hyperstriatum dorsale. It was higher in the hypothalamus than in the hyperstriatum dorsale and higher in the posterior than in the anterior/preoptic hypothalamus.

Aromatase activity in the posterior hypothalamus was higher in males than in females in short-day photosensitive and reproductively active birds, but not in long-day refractory birds. A similar sex difference was also observed in the anterior/preoptic hypothalamus in reproductively active birds.

Hypothalamic aromatase activity in both sexes was directly related to gonadal function, being highest in reproductively active birds and lowest in long-day refractory birds.

It is concluded that the development of long-day refractoriness is not related to an increase in aromatase activity in the neuroendocrine tissues. The decrease in aromatase activity in the neuroendocrine tissues in long-day refractory birds parallels a decrease in aggressive and territorial behaviour.

J. Endocr. (1986) 108, 129–135