Seasonal changes in the plasma testosterone profile in Merino rams

1983 ◽  
Vol 23 (122) ◽  
pp. 254 ◽  
Author(s):  
MJ D'Occhio ◽  
DE Brooks
Keyword(s):  
Seasonal Changes ◽  
Mating Behaviour ◽  
Point Of View ◽  
Plasma Testosterone ◽  
Seasonal Trends ◽  
Testosterone Levels ◽  
Testosterone Secretion

The pattern of testosterone secretion (i.e. profile of plasma testosterone sampled every hour for 24 h) was characterized for Merino rams at various times during the year at latitude 35�S to assess seasonal trends. The profiles of plasma testosterone were always characterized by random peaks regardless of season. However, at any particular time of the year, there were large differences between individual rams in the number of peaks124 h (range 1-7). Mean plasma testosterone levels were higher and a greater number of peaks were recorded per 24 h in summer (December-January) than in winter (July) and spring (September-October). Seasonal changes observed in the plasma testosterone profile of Merino rams were consistent with the concept that activity of the hypothalamic-pituitary-gonadal axis in sheep is entrained to changes in the photoperiod. Merino rams at latitude 35�S are therefore markedly seasonal from an endocrine point of view, although they are not generally regarded as seasonal breeders based on mating behaviour.

scholarly journals Testosterone Does not Increase in Response to Conspecific Challenges in the White-Bellied Antbird (Myrmeciza Longipes), A Resident Tropical Passerine

The Auk ◽  
2006 ◽  
Vol 123 (1) ◽  
pp. 61-66
Author(s):  
Bradley C. Fedy ◽  
Bridget J. M. Stutchbury
Keyword(s):  
Breeding Season ◽  
Temperate Zone ◽  
Plasma Testosterone ◽  
Tropical Species ◽  
Zone Model ◽  
Territorial Aggression ◽  
Social Instability ◽  
Testosterone Levels ◽  
Testosterone Secretion ◽  
Removal Experiments

Abstract Resident tropical passerines that exhibit year-round territorial aggression do not fit well into the temperate-zone model, because testosterone does not increase substantially during the breeding season. We studied patterns of testosterone secretion in the White-bellied Antbird (Myrmeciza longipes), a resident tropical species in Panama that maintains territories year-round and is capable of aggression throughout the year, regardless of its stage of reproduction. Levels of plasma testosterone were low (mean = 0.30 ng mL−1) throughout the breeding and nonbreeding seasons and did not differ between them. Testosterone also did not increase in response to simulated conspecific intrusions. When we used temporary removal experiments to induce natural, extended conflict between males, testosterone levels did not increase in response to the extended social instability that resulted. White-bellied Antbirds demonstrate an apparent uncoupling of testosterone and territorial aggression throughout the year. La Testosterona no Aumenta como Respuesta a Desafíos de Individuos Coespecíficos en Myrmeciza longipes, un Paserino Residente de la Zona Tropical

PLASMA TESTOSTERONE LEVELS IN INTACT AND HEMICASTRATED GROWING COCKERELS

1979 ◽  
Vol 81 (2) ◽  
pp. 169-174 ◽  
Author(s):  
F. J. M. DRIOT ◽  
M. DE REVIERS ◽  
J. WILLIAMS
Keyword(s):  
Plasma Testosterone ◽  
Early Age ◽  
Blood Samples ◽  
Testosterone Levels ◽  
Testosterone Secretion ◽  
Testicular Hypertrophy

Changes in the levels of testosterone in plasma were measured by radioimmunoassay in blood samples taken at frequent intervals between 2 and 26 weeks of age from entire cockerels and cockerels hemicastrated before 2 weeks of age. In both groups the pattern of testosterone secretion could be divided into three clearly defined phases. In young birds, the levels of testosterone in plasma were low (0·3 ng/ml) but in the prepubertal period, at 11 weeks of age, they started to rise and continued to rise until 22 weeks of age when adult levels, which fluctuated between 2·5 and 3·5 ng/ml, were reached. In the immediate period after hemicastration, the concentration of testosterone decreased temporarily. From 11 weeks of age the levels of testosterone in the hemicastrated birds were approximately 75% of those in intact birds. These results are discussed in relation to the compensatory testicular hypertrophy which occurs in growing cockerels hemicastrated at an early age.

Seasonal changes in plasma testosterone concentration and mating activity in Border Leicester, Poll Dorset, Romney and Suffolk rams

1983 ◽  
Vol 23 (122) ◽  
pp. 248 ◽  
Author(s):  
MJ D'Occhio ◽  
DE Brooks
Keyword(s):  
Seasonal Changes ◽  
Extended Period ◽  
Field Conditions ◽  
Plasma Testosterone ◽  
Real Relationship ◽  
Mating Activity ◽  
Testosterone Concentration ◽  
Testosterone Levels ◽  
Seasonal Peak ◽  
Precise Time

Seasonal changes in the plasma testosterone profile and mating activity were compared for Border Leicester, Poll Dorset, Romney and Suffolk rams (three of each breed) maintained under field conditions at latitude 35�S. Border Leicester, Romney and Suffolk showed maximum testosterone levels from February to May. Peak mating activity occurred from March to August, but the precise time and duration of the peak differed between the three breeds. A correlation (r = 0.65, P<0 .05) existed between seasonal changes in plasma testosterone and mating activity in Border Leicester but not in Romney or Suffolk. However, in all three breeds, peak testosterone levels preceded peak mating activity by 1-2 months. Poll Dorset rams showed an extended period of high testosterone levels from August to March but no seasonal peak in mating activity. There was no real relationship, in any breed, between plasma testosterone concentration and mating activity for individual rams within any month.

Seasonal changes in the endocrine responsiveness of the pituitary and testes of male sheep in relation to their patterns of gonadotropic hormone and testosterone secretion

1984 ◽  
Vol 62 (7) ◽  
pp. 827-833 ◽  
Author(s):  
L. M. Sanford ◽  
B. E. Howland ◽  
W. M. Palmer
Keyword(s):  
Seasonal Changes ◽  
Testis Size ◽  
Gonadotropic Hormone ◽  
Testosterone Levels ◽  
Testosterone Secretion ◽  
Testicular Regression ◽  
Serum Hormone ◽  
Lh Release ◽  
Circulating Levels ◽  
Male Sheep

Pituitary and testicular endocrine responses to exogenous gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH), respectively, were assessed for adult rams in an investigation of the regulation of seasonal changes in the patterns of episodic LH and testosterone secretion. Concurrent variations in testis size and in circulating levels of follicle stimulating hormone (FSH) and prolactin (PRL) were also examined. On 10 occasions throughout the year, serum hormone levels were assessed over 6- to 8-h periods during which time rams were left untreated (day 1) or were injected (iv) with single doses of either 10 μg synthetic GnRH (day 2) or 30 μg NIH-LH-S18 (day 3); blood samples were collected from the jugular vein at 10- or 20-min intervals. Testicular redevelopment during the summer, as indicated by increasing testis diameter measurements, was associated with increases in mean FSH level and was preceded by a springtime rise in mean PRL level; "spontaneously" occurring LH pulses and those produced in response to GnRH treatment were relatively large during this period. Increases in the magnitude of testosterone elevations in response to both endogenously and exogenously produced LH pulses occurred in August. Mean testosterone levels were elevated fourfold in the fall as a consequence of relatively frequent and small LH pulses stimulating a more responsive testis to produce more frequent and larger testosterone elevations; endogenous LH pulses, however, did not appear to stimulate the testes maximally at this time. Testicular regression occurred during the winter months and was characterized initially by decreases in testosterone levels without obvious changes in the pattern of pulsatile LH release and subsequently by a decrease in testicular responsiveness to relatively infrequent LH pulses which led to further decreases in testosterone levels and smaller testes. Results demonstrate that alterations in pituitary and testicular responsiveness to stimulatory hormones account in part for seasonal changes in the magnitude of LH and testosterone secretory pulses in adult rams.

Sex steroid levels and Leydig cell ultrastructure of the male common sheath-tail bat, Taphozous georgianus

1989 ◽  
Vol 1 (1) ◽  
pp. 47 ◽  
Author(s):  
SE Jolly ◽  
AW Blackshaw
Keyword(s):  
Leydig Cell ◽  
Seasonal Changes ◽  
Smooth Endoplasmic Reticulum ◽  
Cell Ultrastructure ◽  
Accessory Gland ◽  
Plasma Testosterone ◽  
Reproductive Pattern ◽  
Testosterone Levels ◽  
Accessory Glands ◽  
The Face

Male sheath-tail bats were collected from central Queensland over a 12-month period. Plasma testosterone levels peaked in August, coincident with an increase in the volume of the accessory glands and ampulla/seminal vesicle secretion. Peak spermatogenesis occurred in summer and autumn and declined in the face of maximal testosterone levels in winter. Levels of androstenedione and 5 alpha-dihydrotestosterone were high compared with testosterone levels and showed no significant seasonal changes. Ultrastructural examination of Leydig cell cytoplasm revealed numerous lipid droplets and mitochondria, and an abundant smooth endoplasmic reticulum. There were no seasonal changes in Leydig cell ultrastructure. The anomalous reproductive pattern in this species is consistent with the imposition of a cold-induced winter spermatogenic shutdown, on a framework of continuous spermatogenesis, with spring peaks in testosterone and accessory gland activity.

scholarly journals Role of testosterone and photoperiod on seasonal changes in horn growth and sperm variables in the Iberian ibex: a model for polygynous wild bovids

2012 ◽  
Vol 214 (2) ◽  
pp. 155-163 ◽  
Author(s):  
J Santiago-Moreno ◽  
A Gómez-Brunet ◽  
A Toledano-Díaz ◽  
R Salas-Vega ◽  
F Gómez-Guillamón ◽  
...  
Keyword(s):  
Seasonal Changes ◽  
Growth Regulation ◽  
Day Length ◽  
Plasma Testosterone ◽  
Mating Season ◽  
Capra Pyrenaica ◽  
Testosterone Secretion ◽  
Iberian Ibex ◽  
Horn Growth ◽  
Negative Effect

This work examines the effect of testosterone secretion and photoperiod on seasonal changes in horn growth and sperm variables in the Iberian ibex (Capra pyrenaica), here used as a model for polygynous wild bovids. The hypothesis that high levels of testosterone provide an endocrine signal that inhibits horn growth in autumn was tested by assessing the effect of cyproterone acetate (CA), an anti-androgen, administered in October – coinciding with the period of natural increases in plasma testosterone concentrations – under different photoperiodic conditions (natural photoperiod and artificial long days). The persistence of horn growth during autumn in all ibexes held under the long-day photoperiodic conditions clearly shows that horn growth regulation in the mating season is primarily modulated by day length and not by a fall in testosterone concentration. A retrospectively designed second experiment involving testosterone propionate (TP) administration in April (when horns are growing) was then undertaken to confirm that high levels of testosterone do not inhibit horn growth. Overall, the results strongly suggest that the rise in testosterone secretion during the autumn mating season does not act as an endocrine signal for the arrest of horn growth, although the rate of horn growth before the mating season may be related to springtime testosterone levels. A direct relationship was seen between the rate of horn growth and the incidence of sperm abnormalities. Neither CA treatment in October nor TP administration in April affected the studied sperm variables. By contrast, CA treatment plus artificial long days in autumn had a negative effect on sperm motility and sperm morphology.

Seasonal variation in the plasma testosterone concentration of reindeer and caribou

1973 ◽  
Vol 51 (6) ◽  
pp. 651-658 ◽  
Author(s):  
P. E. Whitehead ◽  
E. H. McEwan
Keyword(s):  
Seasonal Variation ◽  
Growth Pattern ◽  
Seasonal Changes ◽  
Seasonal Pattern ◽  
Plasma Testosterone ◽  
Endocrine Glands ◽  
Testosterone Concentration ◽  
Testosterone Levels ◽  
Rhythmic Growth ◽  
Two Hybrid

Plasma testosterone levels of reindeer increased from 1 ng/cm3 in August to 30–60 ng/cm3 in mid-September. By late October, when rutting activity had almost ceased, the testosterone concentration had declined to barely detectable levels. The seasonal pattern exhibited by caribou was similar except the peak levels associated with rutting occurred about 1 month later than reindeer. The seasonal changes in plasma testosterone levels of two hybrid calves were studied. Peak testosterone levels of 5 and 3.8 ng/cm3 were attained in late October.The influence of the endocrine glands on antler renewal and casting, and the rhythmic growth pattern exhibited by caribou and reindeer are discussed.

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