Bioscientifica Proceedings

Summary. In Exp. 1, sheep fetuses (2 male and 3 female) were gonadectomized between Days 70 and 120 of gestation and their blood LH and FSH levels were compared to those of control animals (4 male, 6 female) at regular times during the first year after birth. In Exp. 2. fetuses (3 male and 5 female) were gonadectomized between Days 50 and 60 of gestation and gonadotrophin levels at Day 90 of gestation were compared to those of control fetuses of the same age. ...

Inhibin, activin and follistatin are protein hormones with diverse physiological roles. The involvement of inhibin in the regulation of pituitary FSH production and secretion in adult males and non-pregnant females is well established. However, it is unlikely that inhibin plays a similar role in pregnancy in ruminants. Inhibin and activin molecules show a high degree of structural similarity to potent growth and differentiation factors of the transforming growth factor β ...

Abstract unavailable© 2009 Society for Reproduction and Fertility...

A major limiting factor in the resumption of postpartum ovarian cycles in cattle is the inhibitory influence of the suckling calf on central regulatory elements controlling the release of GnRH from the median eminence. This inhibitory influence occurs only as a consequence of specifically defined behavioural interactions between the cow and calf in the presence of a maternal bond, cannot be simulated experimentally using thermal, electrical or mechanical stimuli, and is not de...

Summary. The pubertal activation of high-frequency episodic pulses of GnRH is believed to occur as a result of a change in the balance between inhibitory and excitatory stimuli to GnRH neurons. Kisspeptin neurons have been identified as major components of the pathway that regulates GnRH neuronal activity and appear to mediate the effects of estradiol in the control of GnRH secretion. The influence of nutrition on timing the onset of puberty may also involve k...

Summary. The relationship between the pituitary gland and testis in rams was studied from birth to sexual maturity. The concentrations of LH, FSH and testosterone increased between 5 and 7 weeks of age; the rise was not correlated with any specific cytological change in the testis. An augmented pituitary response to LH-RH was demonstrated as levels of gonadotrophin increased. It is unclear whether this change in sensitivity plays a role in initiation of the pu...

Abstract unavailableKeywords: inhibin; male; reproduction; gonadotrophins; FSH© 1991 Journals of Reproduction & Fertility Ltd...

Abstract unavailable© 2009 Society for Reproduction and Fertility...

Abstract unavailableKeywords: inhibin; activin; follistatin. αN peptide; ovary; follicle; corpus luteum© 1991 Journals of Reproduction & Fertility Ltd...

Summary. Phylogenetics is the study of evolutionary relationships among species. Phylogenies are based on the comparison of large numbers of characteristics among species. Traditionally, the field of phylogenetics was dominated by paleontologists so the characteristics studied were structural, often skeletal. The field of phylogenetics was revolutionized in the 1980s as scientists began using molecular data, first amino acid, then nucleotide sequences. This le...