Biomedical subjects

H F Urbanski

Publications and source records attributed to H F Urbanski.

59 records · Page 4Linked to original sources

PubMed1983

Secretion of follicle-stimulating hormone and luteinizing hormone in castrated golden hamsters during exposure to various photoperiods and to natural daylengths.

Golden hamsters were castrated and either maintained under short days of 9 h light and 15 h darkness (9L : 15D) or transferred to 12L : 12D, 13L : 11D or 16L : 8D. Plasma concentrations of FSH and LH remained low under 9L : 15D and 12L : 12D for 6-8 weeks but rose markedly within 4 weeks under 13L : 11D and 16L : 8D, suggesting a more abrupt transition between non-stimulatory and maximally stimulatory photoperiods than found in Japanese quail. Intact and castrated hamsters were exposed to natural photoperiods at a latitude of 51 degrees 27' N (Bristol) for 12 months. In the intact animals plasma FSH and LH levels and the size of the testes decreased as the daylength shortened from 12.5 to 10.5 h during autumn. This was followed by a rise in FSH output in mid-winter with an upward trend in LH secretion. The ensuing testicular recrudescence was complete before the spring equinox. The results emphasize that under natural conditions the primary factor regulating gonadal growth is the development of refractoriness to short days. In castrated hamsters there was no significant seasonal trend in LH output. Levels of FSH remained unchanged until a peak occurred in January, the same time that a peak was seen in intact animals before testicular recrudescence. A similar peak occurred in castrated hamsters maintained in 9L : 15D in the laboratory. This suggests that even in the absence of gonadal steroid negative feedback, hypothalamo-pituitary activity changes during the photorefractory period.

Animals↗

PubMed1982

Photoperiodic suppression of gonadotrophin secretion in castrated male hamsters.

Male golden hamsters were transferred from long to short days and castrated on the day of transfer (Group SP0) or 1, 2 or 3 weeks afterwards (Groups SP1, SP2 & SP3). Animals in Group LP were castrated and maintained on long days. After 7 weeks of short days, plasma levels of LH and FSH were low in Groups SP1, SP2, and SP3. In Group SP0 LH output was also low and FSH secretion, although greater than in Groups SP1, SP2 and SP3, was lower than in the long-day controls (Group LP). This photoperiodic control of gonadotrophin secretion in castrated hamsters raises doubts about the significance of hypothetical alterations in hypothalamo-pituitary sensitivity to sex steroids.

Animals↗

PubMed1982

Photoperiodic modulation of gonadotrophin secretion in castrated Japanese quail.

Male Japanese quail were castrated when sexually immature and immediately exposed to one of the following stimulatory lighting regimes for 52 days: 11 h light: 13 h darkness/day (11L : 13D), 12L : 12D, 13L : 11D, 14L : 10D, 15L : 9D, 16L : 8D, 20L : 4D or 23L : 1D. One group was retained on short days (8L : 16D). Clearcut differences in the plasma levels of LH and FSH emerged between the various groups. Levels remained very low in castrated quail on 8L : 16D but were much greater in those on 14L : 10D, 15L : 9D, 16L : 8D, 20L : 4D and 23L : 1D, eventually becoming 15 to 20 times higher. Less pronounced castration responses developed on 13L : 11D, 12L : 12D or 11L : 13D. Alterations in photoperiod after day 52 caused an appropriate rise or fall in LH secretion. Photoperiodically induced suppressions were rapid, being highly significant within 4 days, but increases usually had a slower time course. When sexually mature quail (on 16L : 8D) were castrated and transferred to 8L :16D they also exhibited a rapid suppression in LH secretion. Thus in quail, unlike some mammals, the photoperiodic control over gonadotrophin secretion is independent of the reproductive status of the animal at the time of castration. The results confirm the view that changes in sensitivity of the hypothalamo-pituitary axis to gonadal steroids are not a primary factor in the neural mechanisms underlying photoperiodism in quail.

Animals↗

PubMed1982

Sexual differentiation of the photoperiodic response in Japanese quail.

Plasma levels of LH are generally higher in male than in female quail. This dimorphism was found to persist in quail which had been through a breeding cycle and then gonadectomized. Under long daylengths (12 h light: 12 h darkness (12L: 12D) or 16L: 8D) ovariectomized quail had plasma levels of LH that were 55-70% of those seen in castrated birds. The difference was reduced after transfer to short days (8L: 16D) when LH concentrations fell to basal levels, but again became more pronounced when the quail were restimulated with long photoperiods. Thus, the photoperiodic response system is sexually differentiated.

Animals↗

PubMedDate not supplied

Neuroendocrine mechanisms controlling the onset of female puberty.

This article describes the major neuroendocrine developments that are associated with the normal onset of puberty in the female rats. Although differences exist between rats and humans with regard to development and function of the reproductive system, there are major basic similarities. This makes the rat a valuable laboratory model in which to evaluate the effects of potentially hazardous substances on normal sexual maturation. A systematic experimental approach is presented to show how the study of reproductive development in the female rat can aid our understanding of the processes by which these substances could disturb normal puberty in the human female.

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