Seasonal variation in serum levels of steroid hormones and their relation with seminal quality and libido in buffalo bulls

Blood samples from 15 breeding male Murrah buffaloes were collected during the winter, summer and monsoon seasons. Seminal characteristics and sexual behaviour were also studied. Serum samples were analysed for testosterone, progesterone and estradiol-17beta levels by radioimmunoassay. The studies showed significantly lower values for testosterone during winter (0.53 +/- 0.06 ng/ml) than during summer (1.22 +/- 0.19 ng/ml) and monsoon (1.06 +/- 0.12 ng/ml). The progesterone level was lowest during monsoon (84 +/- 9 pg/ml), intermediate during winter (115 +/- 14 pg/ml) and highest during summer (224 +/- 24 pg/ml). The mean level of estradiol-17beta was almost double (9 +/- 0.7 pg/ml) during monsoon as compared to winter (5 +/- 0.1 pg/ml). The correlations between hormone levels, seminal characteristics and sexual behaviour were of low magnitude.     

Circulating concentrations of thyroid hormones in pregnant camels (Camelus dromedarius )

Blood samples from 16 female camels were collected at monthly intervals commencing from 60 d post. breeding until the last month of gestation. Two camels failed to conceive and two had unnoticed abortions. The average gestation period was 398+/-13 and 372+/-11 in camels bearing male and female fetus, respectively, with an overall mean of 383+/-9 d. Sera were analyzed for thyroxine (T(4)) and triiodothyronine (T(3)) by radioimmunoassay. Mean T(4) and T(3) concentrations varied from 76 to 116 ng/ml and 0.73 to 1.32 ng/ml, respectively, during various stages of gestation. In general, the T(4) and T(3) levels were higher during early pregnancy, with lowest values in the tenth month. T(4):T(3) ratio showed minor, nonsignificant fluctuations. Age of dam of sex of fetus had no effect on hormone levels. Similarly, hormone levels were not affected by failure of conception or by abortion.     

Exogenous GnRH induces ovulation in seasonally anoestrous lactating goats (Capra hircus)

A specific sheep LH radioimmunoassay was validated for the measurement of goat LH, and used to monitor luteal-phase LH episodes and the preavulatory LH surge in progestagen sponge-synchronized cycling goats. No luteal-phase LH episodes were detected during 12 h of frequent (15-min) blood sampling in 2 goats. A preovulatory LH surge was recorded in 5/5 goats, with a mean amplitude of 45.4 +/- 7.2 ng/ml and a mean time of onset of 38.4 +/- 1.2 h after removal of a progestagen-impregnated sponge. In anoestrous goats, single i.v. injections of 1000 and 2000 ng GnRH induced LH episodes with a mean amplitude of 2.04 +/- 0.11 and 3.67 +/- 0.06 ng/ml respectively, but injections of 250 or 500 ng did not consistently elevate LH concentrations. Progestagen-primed, seasonally anoestrous lactating goats were treated with repeated injections of 1500 ng GnRH (every 2 h for 52 or 78 h) in May 1985 or 1986. All 10 had kidded in March of the same year, and were consequently at peak lactation at the time of GnRH treatment. A preovulatory LH surge was detected in 9 goats with a mean time of onset of 59.5 +/- 2.9 h (1985) or 39.6 +/- 3.3 h (1986) after vaginal sponge removal. All animals displayed oestrus and ovulated, and 9 of the goats were mated: in 5 of these animals pregnancies were successfully carried to term. The results show episodic LH release in response to GnRH and indicate that ovulation can be induced in seasonally anoestrous goats, even at peak lactation, and normal pregnancies may result.     

Hormone concentrations before and after semen-induced ovulation in the bactrian camel (Camelus bactrianus)

During the follicular phase of bactrian camels, basal concentrations of LH were 2.7 +/- 1.2 ng/ml. By 4 h after insemination peak values of 6.9 +/- 1.0 ng/ml occurred. In addition, a smaller LH peak (5.4 +/- 2.5 ng/ml) appeared 1 day before regression of the follicle began in unmated camels. During the follicular phase peripheral plasma progesterone values were low (0.36 +/- 0.28 ng/ml), but values increased to reach 1.73 +/- 0.74 ng/ml at 3 days and 2.4 +/- 0.86 ng/ml at 7 days after ovulation. Plasma oestradiol-17 beta concentrations were 26.8 +/- 9.0 pg/ml during the follicular phase and 30.8 +/- 5.1 pg/ml when the follicle was maximum size. Values fell after ovulation but rose to 29.8 +/- 6.5 pg/ml 3 days later.     

Seasonal variations in plasma hormones and reproductive efficiency in early postpartum buffalo

Investigations were carried out on twenty newly calved Murrah buffalo that were divided into two sets of ten each during winter (December to February) and summer (May to September). Recommended feeding and management practices were followed. Blood samples were collected on Days 0, 1, 2, 4, 6, 8, 15, 22, 29, 36, 43, 50 and 57 postpartum for hormone radioimmune assay (RIA). The values of reproductive parameters and hormone levels during winter and summer, respectively, were the following for uterine involution, 39.50 +/- 2.74 d and 32.50 +/- 3.01 d; first postpartum estrus interval, 70.10 +/- 9.62 d and 37.40 +/- 11.82 d; number of services per conception, 1.57 +/- 0.29 and 2.40 +/- 0.68; first service conception rate, 40 and 20 %, overall conception rate, 70 and 40 %; 13,14-Dihydro-15-keto prostaglandin F(2alpha) (PGFM), 1.78 +/- 0.26 ng/ml and 2.62 +/- 0.30 ng/ml; progesterone, 1.09 +/- 0.14 ng/ml and 0.65 +/- 0.77 ng/ml. A negative correlation (r = -0.83, P 0.05 ) was observed between PGFM and progesterone. Although, summer stress hastens uterine involution and first postpartum estrus interval, overall reproductive efficiency is impaired due to deficiency of progesterone, which is essential for embryo survival.     

Peripheral inhibin levels in relation to climatic variations and stage of estrous cycle in buffalo (Bubalus bubalis )

The present study investigated the peripheral plasma inhibin levels in relation to 1) the stage of estrous cycle and the effect of climatic variations. Blood samples were collected from cyclic buffalo (n=5) once daily for 32 consecutive days during the tropical hot humid (summer) and cold (winter) seasons. Estrus was recorded by parading a vasectomized bull as well as by plasma progesterone determination. In the winter season, peripheral inhibin concentrations which were lowest (0.35 +/- 0.02 ng/ml) during the mid-luteal phase of estrous cycle (Day 6 to Day 14, Day 0 = day of estrus) increased significantly (P < 0.02) to 0.47 +/- 0.04 ng/ml during the late luteal phase (Day -4 to Day -2) and then further to 0.52 +/- 0.03 ng/ml (P< 0.02) during the periestrus phase (Day -1 to Day 1). Inhibin concentrations then decreased significantly (P < 0.02) to 0.40 +/- 0.03 ng/ml during the early luteal phase (Day 2 to Day 5). In the summer season the differences in peripheral inhibin concentrations among different phases of estrous cycle were found to be nonsignificant. A comparison of the circulating inhibin concentrations between the two seasons indicated that inhibin concentrations were significantly higher in the late luteal phase (P < 0.01) and periestrus phase (P < 0.05) during the winter season compared with corresponding periods during the summer season. The present study suggests that peripheral inhibin concentrations change in the estrous cycle during cooler breeding season and that environmental heat stress can cause a reduction in peripheral inhibin concentrations.     

Induction of luteal activity and progesterone secretion in the nonpregnant one-humped camel (Camelus dromedarius)

Corpora lutea (n = 20) were detected in 5 one-humped female camels studied during a period of 4 months. Complete mating by a vasectomized male, male introduction into the pen of females without mating, or a progesterone decrease from a previous corpus luteum were followed by a similar progesterone pattern. A maximal plasma concentration of 4.5 +/- 1.5 ng progesterone/ml (2.7-8.8 ng/ml) occurred 8.55 +/- 1.32 days (6-11 days) after the inducing stimulus. Luteal regression, beginning 8.65 +/- 1.18 days after the stimulus, was completed at Day 11.55 +/- 1.05. Morphological development of ovarian structures, detected by rectal palpation, was in synchrony with the progesterone increase, but there was a prolonged period of regression. Females accepted mating up to 7 days after the ovulatory stimulus, when progesterone levels were as high as 3.5 ng/ml. This study establishes the absence of pseudopregnancy in the one-humped female camel, and offers opportunities for improving the management of reproduction. It also shows that ovulatory stimuli other than mating can be effective in these animals.     

Relation between progesterone concentrations during the early luteal phase and follicular dynamics in goats

We studied the relationship between progesterone (P4) concentrations early in the estrus cycle and follicular dynamics in dairy goats. We used seven untreated goats (control group) and six progesterone treated goats (P group) with a controlled internal drug release device from Days 0 to 5 (Day 0: day of ovulation). We performed daily ultrasonograph during the interovulatory interval to determine ovarian change and took daily blood samples to determine serum estradiol 17beta (E2) and P4 concentrations by RIA. We divided the control goats into 3- (n = 4) and 4-wave goats (n = 3), according to the number of follicular waves recorded during the ovulatory cycle. Mean progesterone concentrations between Days I and 5 were higher and mean estradiol concentrations between Days 3 and 5 were lower in 4-wave goats (P4: 3.8+/-0.2 ng/ml; E2: 1.6+/-0.2 pg/ml) than in 3-wave goats (P4: 2.0+/-0.5 ng/ml, P < 0.05; E2: 4.4+/-0.9 pg/ml, P < 0.05). Wave 2 emerged earlier in 4-wave (Day 4.2+/-0.3) than in 3-wave goats (Day 7.3+/-0.3, P < 0.05). Three out of six of the progesterone-treated goats had short cycles (mean 8.0+/-0.0 days) and ovulated from Wave 1. The other three goats had shorter cycles (mean 18.3+/-0.3 days) than the control group (20.0+/-0.2 days; P < 0.05), although they were within the normal range of control cycles (shortened cycles). In the three treated goats with shortened cycles (two with four waves, one with three waves), mean progesterone concentrations between Days I and 5 were higher (4.7+/-0.6 ng/ml) than in the 3-wave control goats. In these goats, Wave 2 emerged at Day 4.3+/-0.3, similar to the time observed in 4-wave goats but earlier (P < or = 0.05) than in 3-wave control goats. Overall results confirm a relationship between the progesterone levels and the follicular wave turnover during the early luteal phase in the goat. Higher progesterone concentrations may accelerate follicular turnover probably by an early decline of the negative feedback action of the largest follicle of Wave 1. This is followed by an early emergence of Wave 2.     

Effect of GnRH antagonists treatment on gonadotrophin secretion, follicular development and inhibin A secretion in goats

The aim of this study was to determine, for goats, the effects of daily doses of GnRH antagonist on ovarian endocrine and follicular function. Ten does were given 45 mg FGA intravaginal sponges and then five were treated with daily injections of 0.5mg of the GnRH antagonist Teverelix for 11 days from 2 days after the day of sponge insertion, while five does acted as controls. Pituitary activity was monitored by measuring plasma FSH and LH daily from 2 days before the first GnRH injection to Day 12. Follicular activity was determined by ultrasonographic monitoring and by assessing plasma inhibin A levels during the same period. In treated does, the FSH levels decreased linearly (0.8 +/- 0.1 ng/ml to 0.5 +/- 0.1 ng/ml, P < 0.01) and remained lower than the mean concentration in control goats (0.8 +/- 0.1 ng/ml, P < 0.005). LH levels were also lower during the period of antagonist treatment (0.6 +/- 0.2 ng/ml versus 0.4 +/- 0.1 ng/ml, P < 0.0005). During GnRH antagonist treatment, there was a significant decrease in the number of large follicles (> or = 6 mm) from Day 3 of treatment (1.2 +/- 0.6, P < 0.0001), with no large follicles from Day 9. The number of medium follicles (4-5 mm in size) also decrease during the period of treatment (4.2 +/- 0.7 to 1.0 +/- 0.6, P < 0.0001), leading to a significant decrease in inhibin A levels when compared to the control (143.7 +/- 31.3 pg/ml versus 65.2 +/- 19.1 pg/ml, P < 0.00005). In contrast, the number of small follicles (2-3 mm) increased in treated goats from Day 4 of treatment (9.6 +/- 2.9 to 20.2 +/- 6.3, P < 0.005). Such data indicate that GnRH antagonist reduced plasma levels of FSH and LH with suppression of the growth of large dominant ovarian follicles and a two-fold increase in number of smaller follicles. The results confirm that GnRH antagonist treatment can be used in goats to control gonadotrophin secretion and ovarian follicle growth in superovulatory regimes.     

Studies on the growth of the fetal sheep. Effects of surgical reduction in placental size, or experimental manipulation of uterine blood flow on plasma sulphation promoting activity and on the concentration of insulin-like growth factors I and II

The effect of long- and short-term manipulations of uterine blood flow on fetal plasma levels of IGF-I and -II have been studied in sheep at days 125-139 of pregnancy and compared with those in near term rats and guinea pig. The primary objective is to show that both long- and short-term reduction of uterine blood flow is associated with increase in the fetal plasma concentration of IGF-II while that of IGF-I falls. In the pregnant sheep long-term depression of utero-placental blood flow was caused by surgical reduction in placental mass (carunclectomy) prior to conception. This reduced fetal weight to 2.42 +/- 0.49 kg (SD) compared with 3.41 +/- 0.46 in controls; the respective values for uterine blood flow being 1694 +/- 558 and 913 +/- 324 ml/min respectively. This was associated with a fall in fetal plasma IGF-I concentration from 22.6 +/- 3.4 ng/ml to 14.9 +/- 1.31 ng/ml and a rise in IGF-II from 1952 +/- 284 ng/ml to 3360 +/- 914 ng/ml respectively. Similar changes in the plasma concentrations of IGF peptides were observed in fetal rats and guinea pigs in response to uterine artery ligation. Short-term reduction (60 min) of the uterine blood flow was caused either by compression of the common uterine artery to depress flow from 1491 +/- 375 to 648 +/- 216 ml/min or through intraarterial infusion of adrenaline at 35 ug/min to lower flow from 1628 +/- 339 to 1195 +/- 128 ml/min. Such falls in uterine blood flow had no significant effect on fetal plasma IGF-I levels but increased IGF-II levels by 30 to 60%.     

Further studies on prevalence of hydatidosis in slaughtered animals from North Jordan

Examination of 471 sheep, 118 goats, 157 cattle and 56 camels slaughtered in abattoirs in North Jordan was carried out during March-May 1984. Drought conditions that prevailed during the preceding winter led to slaughtering old female sheep (greater than or equal to 4 years) due to scarcity of food, which allowed us to analyse the prevalence of hydatidosis in various age groups of sheep. An overall infection rate of 27.8, 1.7, 5.8 and 10.7 percent was found in sheep, goats, cattle and camels, respectively. The infection rate was as low as 1.5 percent in male and 1.9 percent in female sheep under 2 years of age. However, the rate of hydatid infection increased with age and reached as high as 63.7 percent in ewes 4 years of age and older. The percentage of animals with fertile cysts was also highest in sheep (68.7 percent of infected animals) and increased with age reaching 100 percent in ewes which were 10 years of age or older. Analysis of all cysts recovered from the livers and lungs of infected ewes from various age groups revealed a sharp increase in the mean total number of cysts in age groups over 8 years of age. The fertility rate of the cysts in the liver was significantly greater in ewes 6 years old or more (64.8--78.6 percent) than in younger age groups (8.7-46.2 percent). In the lung, the fertility rate increased progressively with age reaching as high as 97.9 percent in ewes 10 years old or more. These findings of high infection and fertility rates of hydatid disease in sheep, particularly of older age groups, prompt plans for further epidemiological studies and control programmes.     

A comparative study of glycosylated haemoglobin level in the Arabian camel (Camelus dromedarius) during different seasons

1. The extent of haemoglobin glycosylation from 60 camels has been determined (4.39%) in blood samples drawn during winter. 2. Phosphate (9.45 mg/dl), DPG (2.9 mumol/ml) and glucose (138 mg/dl) levels were also recorded. 3. In addition the P50 at pH 7.4 was measured (22.8 Torrs). 4. The data obtained compared with human blood levels and with levels reported for camels during summer sampling. 5. Despite the fact that camels have higher blood glucose levels than humans, the extent of glycosylation is much less in camel blood than in human blood.     

Age-related changes in plasma testosterone concentrations and genital organs content of bulk and trace elements in the male dromedary camel

There is a paucity of information regarding the influence of plasma testosterone concentrations and inorganic cations secreted in the different seminal fractions on the spermatozoon activity throughout the reproductive life of the one-humped camels. To demonstrate these relationships, the genital organs of 12 prepubertal (<3 years), 9 peripubertal (3-<5 years), 16 mature (5-<15 years) and 15 aged (>/=15 years) camels were collected from the Buraidah slaughter house (Al-Qassim Province, Saudi Arabia) during two consecutive breeding seasons (November-April) over 2 years. Plasma testosterone concentrations (mean+/-S.E.) did not exceed 1.4 ng/ml in prepubertal animals with a 3-4 fold increase in peripubertal (3.2+/-0.4 ng/ml) and mature (4.8+/-0.6 ng/ml) camels followed by about 50% decrease (2.6+/-0.3 ng/ml) in aged ones. These hormonal changes were correlated significantly with concentrations of certain elements in the testes (highest Na, Ca and Cu contents), epididymides (highest P and Fe contents), prostate (highest Zn content), and bulbo-urethral glands (highest K and Mg contents). The significance of some interrelationships among the different cations and their biological effects on sperm production and metabolic activity were discussed.     

Concentrations of testosterone and androsterone in peripheral and umbilical venous plasma of fetal rats

Mean +/- s.d. testosterone concentrations in the peripheral plasma of 21- and 22-day-old male fetuses (1.32 +/- 0.43 ng/ml) were significantly (P less than 0.05) higher than those in the umbilical venous plasma (0.37 +/- 0.08 ng/ml). Testosterone concentrations in umbilical venous plasma of male and female (0.29 +/- 0.06 ng/ml) fetuses and in peripheral plasma of female fetuses (0.36 +/- 0.10 ng/ml) were not significantly different. Androsterone levels measured in umbilical venous plasma of male (11.5 +/- 2.5 ng/ml) and female (12.3 +/- 2.1 ng/ml) fetuses were nearly as high as those in peripheral plasma (males, 12.9 +/- 3.1; females, 13.3 +/- 3.5 ng/ml). There were high concentrations of androsterone in the placentas of male (33 +/- 4 ng/g) and female (33 +/- 5 ng/ml) fetuses, suggesting that this organ is the major source of fetal androsterone. We also conclude that a major part of the testosterone present in female fetuses is secreted by the placentas.     

Restoration of endocrine and ovarian function after stopping GnRH antagonist treatment in goats

We have tested if the high number of unfertilized ova and degenerated embryos found in superovulated goats previously treated with GnRH antagonist can be related to a prolongation of gonadotrophin down-regulation and/or alterations in follicular function during the period of administration of the superovulatory treatment, around 4 days after the end of the antagonist treatment. A total of 15 does were treated with intravaginal progestagen sponges and daily injections of 0.5mg of the GnRH antagonist Antarelix for 6 days, while 5 does acted as controls receiving saline. During the antagonist treatment, the mean plasma LH concentration was lower in treated than control goats (0.5 +/- 0.2 versus 0.7 +/- 0.5 ng/ml, P < 0.0005 ); however, the FSH levels remained unaffected (0.8 +/- 0.4 versus 0.8 +/- 0.5 ng/ml). In this period, treated does also showed an increase in the number of small follicles with 2-3 mm in size ( 10.7 +/- 0.7 versus 8.4 +/- 0.6, P < 0.05), and a decrease in both the number of follicles > or =4 mm in size ( 5.0 +/- 0.3 versus 6.8 +/- 0.5, P < 0.005) and the secretion of inhibin A (120.9 +/- 10.7 versus 151.6 +/- 12.6 pg/ml, P < 0.05). After cessation of the antagonist treatment, there was an increase in LH levels in treated goats from the day after the last Antarelix injection (Day 1), so that LH levels were the same as controls on Day 3 (0.6 +/- 0.1 versus 0.6 +/- 0.2 ng/ml). However, there were even greater numbers of small follicles than during the period of antagonist injections (15.4 +/- 0.6 in treated versus 8.9 +/- 0.7 in control, P < 0.0005 ). Moreover, the number of > or =4 mm follicles and the secretion of inhibin A remained lower in treated goats (3.9 +/- 0.3 follicles and 84.4 +/- 7.0 pg/ml versus 5.4 +/- 0.5 follicles, P < 0.05 and 128.9 +/- 14.2 pg/ml, P < 0.05 ). These results indicate that pituitary secretion of gonadotrophins is restored shortly after the end of antagonist treatment, but activity of ovarian follicles is affected.     

Seasonality of plasma testosterone in males of four Mediterranean goat breeds and in three different climatic conditions

The aims of the present work were to evaluate if a seasonality of plasma testosterone concentrations exists in Mediterranean male goats and it may be affected by climatic conditions. Testosterone concentrations were determined throughout 1 year in blood samples collected weekly from 24 males of 4 Mediterranean goat breeds (Ionica, Garganica, Maltese and Red Syrian), fed a constant diet, maintained without interactions with does and reared in 3 farms with different climates, in Italy. Plasma testosterone concentrations were affected by season (P<0.0001), being higher during summer (8.33+/-0.35 ng/mL) than during autumn (6.81+/-0.26 ng/mL), which were in turn higher than in winter (1.55+/-0.08 ng/mL) and spring (2.04+/-0.15 ng/mL). An effect of breed was recorded (P<0.001), Ionica bucks having the highest plasma testosterone means, Red Syrian and Maltese the lowest. The onset of the reproductive season was similar among the breeds. Ionica bucks had a later offset than Red Syrian and Maltese and a longer reproductive season than Maltese bucks (P<0.05). No effect of farm nor interaction breed x farm was recorded. Single sporadic peaks of plasma testosterone were recorded in many bucks, outside the main reproductive season, especially during spring. In conclusion the bucks of all the four breeds displayed a clear seasonality of plasma testosterone, with very low levels from January to May and high levels from July to November; hormone levels and pattern of seasonality were affected by breed and not by climate.     

Timing of sexual maturity in female rhesus monkeys (Macaca mulatta) housed outdoors

A comparison of the age and season at first parturition was made for spring-born female rhesus monkeys and for females born in the fall to mothers who had been laboratory-housed before being transferred outdoors. Females (N = 9) born during the fall had first parturition during the spring and summer, as did all spring-born females (N = 68), and not during the fall as would be predicted if age were the determining factor. A separate analysis of post-menarchial, spring-born females (N = 5) beginning in September at 29 months of age revealed that the ensuing 12 months were characterized by low serum levels of oestradiol (less than 50 pg/ml), progesterone (less than 1.0 ng/ml), LH (less than 7.0 ng/ml), and FSH (less than 5.50 micrograms/ml). First ovulation subsequently occurred in the fall in all subjects at a mean age of 41.9 +/- 0.1 months, and was preceded by significant elevations in basal LH and FSH, coincident in time with the transition of summer to fall (September). Female copulatory behaviour was restricted to the period surrounding first ovulation, beginning some 2 weeks before and ceasing within 3 days after the oestradiol peak. The most rapid gain in weight occurred during the summer months before first ovulation, and was associated with significant elevations in serum GH and prolactin. These data suggest that season may influence the timing of sexual maturation in rhesus monkeys kept outside in such a way that the occurrence of first ovulation is restricted to the fall and winter months.     

Haemonchus longistipes Railliet & Henry, 1909 in goats in the Sudan

Haemonchus longistipes specimens were collected from experimentally infected Sudanese goats and camels for morphological studies. The specimens from goats were much smaller than those from camels, but their infectivity to camels was not affected by their passage in goats. Goats inhabiting the same areas as camels in the Sudan were found to be naturally infected with H. longistipes, but sheep were not and were resistant to experimental infection.     

Effect of fasting on luteal function, leptin and steroids concentration during oestrous cycle of the goat in natural photo-status

The effect of fasting during oestrous cycle on the occurrence of oestrous and concentration of leptin and steroid hormones was investigated in goats. Sixteen Ardi goats of 10-12 month of age were split into two groups (control and fasting). Oestrous was synchronized with intravaginal progesterone sponges and detected 24h after sponge removal. Blood samples were collected at the days 5, 10, 15 of each cycle. Fasting of mature goats twice for 4 days starting on day 10 of two successive oestrous cycles inhibited oestrous behaviour and resulted in reduced concentration of leptin, progesterone and testosterone with different timing. Day 5 of the second cycle showed significant decrease in the plasma level of leptin (1.6+/-0.15 ng/ml) and progesterone (1.6+/-0.1 ng/ml) as compared to control group (3.2+/-0.15 ng/ml and 4.1+/-0.2 ng/ml, respectively). Testosterone started to decrease from day 10 of the second cycle (35.0+/-12.0 pg/ml) as compared to control group (65.0+/-15.0 pg/ml); the decrease in this hormone was significant in day 15 of the second cycle (65.0+/-16.0 pg/ml) as compared to the control (320.0+/-50.0 pg/ml). These data suggest that fasting-induced inadequate corpus luteum function, hence, lowering progesterone plasma level may partly be more leptin-dependent than the following decrease in plasma level of testosterone.     

Seasonal changes in testicular contents and plasma concentrations of androgens in the desert gerbil (Gerbillus gerbillus)

Gerbils were caught in the Béni-Abbès area (Algeria). Testicular endocrine activity was highest in spring (testicular wt 298 +/- 10 mg; seminal vesicle wt 603 +/- 62 mg; testicular testosterone and androstenedione content 9.2 +/- 1.7 and 0.5 +/- 0.1 ng/testis; plasma testosterone 832 +/- 200 pg/ml). Values decreased in summer, were lowest in late summer and in autumn (84 +/- 17 mg; 40 +/- 14 mg; 0.20 +/- 0.06 and 0.02 +/- 0.01 ng/testis; 228 +/- 54 pg/ml, respectively) and increased again in winter (December-January). The onset of testicular endocrine activity was concomitant with the lowest temperatures and the shortest photoperiod; it increased when temperatures and daylength were increasing and began to decline when temperatures and photoperiod were still maximal. These seasonal changes in the endocrine activity of the testis of the gerbil differ from those of the sand rat inhabiting the same area.