PubMed Health⌕ Search

Biomedical subjects

C L Adam

Publications and source records attributed to C L Adam.

At least 37 records · Page 2Linked to original sources
PubMed1998

Effects of insulin-like growth factor-1 on luteinizing hormone secretion in sheep.

Circulating insulin-like growth factor-1 (IGF-1) may be involved in nutritional modulation of reproductive status. Acute effects of IGF-1 on luteinizing hormone (LH) secretion were studied in two experiments, each using eight castrate male sheep surgically prepared with an elevated carotid artery, four with (E+) and four without (E-) subcutaneous oestradiol implants. Blood samples were taken every 12 min for 8 h at weekly intervals, with IGF-1 given at 4 h. In Experiment 1, sheep were fed to maintain live weight (maintenance) and IGF-1 doses tested were 25, 50, 100 and 150 micrograms kg-1 given via the carotid (i.c.). Plasma LH concentrations were 6.2 +/- 0.35 (E-) and 4.2 +/- 0.49 (E+) ng ml-1 pre-IGF-1, were increased after 25 micrograms kg-1 IGF-1 (E-, 15%; E+, 11%) but were either unaltered (E-) or decreased (E+, -16%) after 150 micrograms kg-1; thus, mean LH response was negatively related to IGF-1 dose (E-, b = -0.007, P < 0.01; E+, b = -0.011, P < 0.05). LH pulse frequencies (p.f.) were 4.6 +/- 0.42 (E-) and 3.9 +/- 0.35 (E+) pulses per 4 h pre-IGF-1, were unaltered after 25 micrograms kg-1 IGF-1, but were decreased after 150 micrograms kg-1 (E-, -33%; E+, -51%); thus, p.f. was also negatively related to IGF-1 dose (E-, b = -0.016, P < 0.01; E+, b = -0.019, P > 0.05). LH pulse amplitude and baseline were not significantly altered by IGF-1. Plasma glucose concentrations decreased after 100 and 150 micrograms kg-1 IGF-1 from 3.40 to 2.50 and 2.34 mmol l-1, respectively (SED 0.314, P < 0.001), but were not significantly altered after lower doses. Thus, hypoglycaemia caused LH inhibition after higher doses of IGF-1, which counteracted (E-) or overcame (E+) the stimulatory effects on LH seen after lower doses. In Experiment 2, sheep were fed 50% maintenance; saline vehicle i.c., then IGF-1 doses 25 and 50 micrograms kg-1 given i.c. or i.v. were tested. In E- and E+ sheep, respectively, mean LH pre-IGF-1 was 8.7 +/- 0.97 and 1.9 +/- 0.16 ng ml-1, p.f. was 3.8 +/- 0.44 and 0.8 +/- 0.44 pulses per 4 h, and amplitude was 3.6 +/- 0.49 and 0.4 +/- 0.08 ng ml-1. Saline vehicle had no effect on LH. IGF-1 at both doses and by both administration routes in E- sheep increased mean LH (22-29%, P < 0.001), and in E+ sheep increased mean LH (12-36%, P < 0.001), p.f. (94-219%, P < 0.001) and amplitude (125-803%, P < 0.01). Thus, low doses of peripherally-administered IGF-1 stimulated LH output in sheep, consistent with its putative physiological role as a nutritional modulator of reproduction.

Animals↗
PubMed1998

Inhibition of luteinizing hormone secretion and expression of c-fos and corticotrophin-releasing factor genes in the paraventricular nucleus during insulin-induced hypoglycaemia in sheep.

Insulin can act within the brain to stimulate ovine luteinizing hormone (LH) secretion, but insulin-induced hypoglycaemia inhibits LH via unknown brain sites, possibly involving corticotrophin-releasing factor (CRF). Castrate male sheep, with (E+) or without (E-) subcutaneous oestradiol implants, were blood sampled every 12 min for 8 h. Insulin (0.25 or 0.5 IU/kg) was injected at 4 h via the carotid artery or jugular vein. All treatments reduced LH output with no differences between dose rate nor route of administration, but sensitivity was greater in E+ than E-sheep. There was no evidence for an effect of insulin on LH 0-1 h postinjection; however, 1-3 h after insulin, when hypoglycaemia was established, LH pulses were inhibited in both E+ and E- sheep (P<0.001). Additional intravenous (i.v.) glucose injections given 1 h (20 mmol) and 2 h (10 mmol) after insulin (0.5 IU/kg) were each followed by an LH pulse within 30 min (75% response in both E+ and E-sheep). In a separate experiment, sheep were killed 2 h after i.v. insulin (0.5 IU/kg) or saline. In-situ hybridization revealed c-fos mRNA in the paraventricular nucleus (PVN), but not in any other hypothalamic nuclei nor in the hindbrain; and this was linked with increased CRF gene expression in the PVN. Similar c-fos and CRF gene expression was seen in insulin-treated sheep given additional i.v. glucose (20 and 10 mmol, respectively, 40 and 20 min ante mortem), but not in saline-treated controls. Therefore, insulin-induced hypoglycaemia inhibited LH secretion, with oestradiol potentiating the effect, and was associated with gonadal steroid-independent c-fos gene expression and increased CRF gene expression in the PVN. The ovine PVN may be involved in mediating insulin-induced hypoglycaemic inhibition of LH by a mechanism which might involve CRF.

Animals↗
PubMed1998

Effect of restricted nutrition on timing of puberty in female Soay sheep.

Ovariectomized, oestradiol-implanted Soay ewe lambs from 21 September (aged 21 weeks) had restricted (liveweight maintenance) (n = 4) or unrestricted food (n = 4); ovary-intact lambs had unrestricted food (n = 8). LH activation in ovariectomized lambs on restricted and unrestricted food and onset of ovulatory cycles in ovary-intact lambs all occurred on 7 December (SED 8.8 days) (32 weeks), but at different liveweights (24.2, 17.9 and 18.3 kg, respectively, SED 1.22). LH pulse frequency was similar in ovariectomized lambs on restricted and unrestricted food. From 29 August (aged 18 weeks), Soay ewe lambs in seasonally advanced decreased artificial daylength were given restricted food, unrestricted food, or food was restricted for 8 weeks and then unrestricted (n = 8 per group). Ovarian cycles started 3 weeks earlier than in lambs in natural photoperiod on similar dates for all three groups (14, 18 and 19 November, respectively, SED 5.5 days) (29 weeks), but at different liveweights (16.2, 20.7, and 18.4 kg, respectively, SED 0.87). From 1 August, Suffolk x Greyface ewe lambs (aged 16 weeks) had restricted food, unrestricted food, or food restricted for 8 weeks and then unrestricted (n = 8 per group). By 1 November (29 weeks), 0/8 lambs on restricted food (29.3 +/- 0.92 kg) but 8/8 lambs on unrestricted food an 5/8 lambs on 8 weeks of restricted food had ovulated (mean dates: 16 October +/- 2.5 days (27 weeks, 40.1 +/- 1.02 kg), and 1 November +/- 3.0 days (29 weeks, 35.5 +/- 1.23 kg), respectively. Thus, nutritional growth restriction during the 11 weeks preceding normal puberty delayed pubertal data in the improved breed but did not influence the timing of puberty in the unimproved Soay breed within the weight range studied.

Animal Nutritional Physiological Phenomena↗
PubMed1998

Estimation of energy expenditure in free-living red deer (Cervus elaphus) with the doubly-labelled water method.

Energy expenditure was estimated using the doubly-labelled water (DLW) method in summer in five free-living adult, non-pregnant, non-lactating, red deer (Cervus elaphus) hinds (weight 107.3 (SE 0.9) kg; age 6 (SE 1) years) on lowland pasture under typical farming conditions. Climatic conditions were monitored throughout the experiment. Errors due to 2H losses in CH4 and faeces were calculated from previous estimates of stoichiometries. CH4 production, fractionated water loss, urinary N and O2 consumption were estimated using an iterative approach. The water flux (rH2O) in these animals consuming only fresh grass was 12 (SE 0.5) kg/d, the CO2 production (rCO2) was 1271 (SE 40) litres/d and the mean energy expenditure was 25 (SE 0.8) MJ/d. There were no significant differences in the isotope distribution spaces and flux rates, rH2O, rCO2 or energy expenditure using the multi-point or two-point approaches to calculation. The DLW-derived energy expenditure of 25 MJ/d is approximately 20% higher than the recommended intake of 21 MJ/d for adult hinds kept outdoors (Adam, 1986) and, at 757 kJ/kg0.75 per d, one third higher than the value of 570 kJ/kg0.75 per d for stags penned indoors (Key et al. 1984).

Animals↗
PubMed1997

Melatonin receptors in red deer fetuses (Cervus elaphus).

Red deer (Cervus elaphus) exhibit highly seasonal rhythms in physiology and behaviour. The influence of photoperiod on the timing of these changes begins in utero where the fetus receives photoperiodic information via the diurnal pattern of maternal melatonin secretion. The potential sensitivity of deer fetuses to melatonin was ascertained by mapping specific receptors and characterizing them using 2-[125I]iodomelatonin and quantitative autoradiography in vitro. Specific binding occurred from day 31 of gestation onwards (term = 233 days) over the spinal nerves and respiratory system. At later stages of gestation binding occurred over the brain, particularly the brainstem, the pituitary gland, thyroid gland, gastrointestinal tract including the pancreas, metanephros, cochlea of the ear, spinal cord, and spinal and cranial nerves. Binding was abolished in the presence of 10(-7) mol melatonin l-1 and diminished in the presence of 10(-4) mol GTP gamma S l-1 (guanosine-5-O-(3-thiotriphosphate)), confirming that binding represented functional G-protein-coupled melatonin receptors. Characterization studies, carried out on fetal lung, revealed that binding was time-dependent, reaching equilibrium at about 3 h at room temperature (22 degrees C), and saturable with a dissociation constant (Kd) of 104 pmol l-1. This study demonstrates the presence of G-protein-coupled melatonin receptors over a wide range of tissues in red deer fetuses from early in gestation, indicating that in addition to its role in the communication of photoperiodic information to the fetus in this species, melatonin may be involved in fetal growth and development.

Animals↗
PubMed1997

Effect of nutrition on testicular growth and plasma concentrations of gonadotrophins, testosterone and insulin-like growth factor I (IGF-I) in pubertal male Soay sheep.

Nutritional effects on puberty were studied in Soay rams. Testicular growth is initiated at birth in April and testes reach maximum size in October. Groups of eight lambs were fed for 18 weeks, starting in August, a ration that restricted growth (Group R), the same diet ad libitum (Group F), or a restricted diet for 8 weeks followed by ad libitum feeding (Group R/F). Seasonal increases of plasma FSH, testis size, sexual skin flush and plasma testosterone occurred with similar timing but reduced magnitude in Group R compared with Group F lambs. Testis size and sexual skin flush peaked in all groups at 11 weeks (30 October); the testes of Group F animals were larger before the peak, but similar in size thereafter, compared with testes from Group R/F, and larger throughout the experimental period than testes from Group R. Plasma testosterone was higher in Group F than in Group R lambs from 7 to 17 weeks, but in Group R/F was similar to Group R before 10 weeks (23 October) and similar to Group F thereafter. Testis size, plasma testosterone, plasma insulin-like growth factor I (IGF-I) and liveweight were positively correlated. Ad libitum feeding in August-September (Group F) stimulated increased plasma FSH and LH above values for Group R, but ad libitum feeding initiated in October did not affect gonadotrophin concentrations (Group R/F). Therefore, the effects of improved nutrition on the hypothalamo-pituitary axis, which may have been mediated by circulating IGF-I, were season- or age-dependent, and those on the testes included direct stimulation, independent of changes in gonadotrophin concentrations. Nutrition modified the intensity, but not the timing, of peak pubertal reproductive activation.

Animal Nutritional Physiological Phenomena↗
PubMed1997

Effect of chronic food restriction on pulsatile luteinizing hormone secretion and hypothalamic neuropeptide Y gene expression in castrate male sheep.

Castrate male sheep (wethers, average liveweight 38 +/- 0.6 kg) were given one of the following diets for 10 weeks followed by euthanasia (n = 8/group): high-energy high-protein providing 1-5 times the energy required to maintain liveweight (maintenance) (group 1.5 M), low-energy low-protein at 0.5 maintenance (0.5 M), or low-energy high-protein at 0.5 maintenance (0.5 M + P). 1.5 M wethers gained 22% liveweight whereas 0.5 M and 0.5 M + P wethers lost 18 and 13% liveweight respectively. Relative to the 1.5 M group, the 0.5 M and 0.5 M + P groups had similar plasma concentrations of glucose and cortisol throughout, but elevated non-esterified fatty acids (P < 0.001) and reduced IGF-I and insulin (P < 0.05, 0.01 or 0.001) from 1 week onwards. Each week blood samples were taken every 12 min for 4 h and plasma assayed for LH. Mean concentration over 4 h, LH pulse frequency and LH pulse amplitude showed no progressive change in 1.5 M sheep. However, in both 0.5 M and 0.5 M + P groups mean LH increased (P < 0.001 and P < 0.01 respectively), pulse frequency decreased (P < 0.01 and P < 0.01) and pulse amplitude increased (P < 0.001 and P < 0.01) over the 10-week period. Anterior pituitary. LH content was greater in 0.5 M (P < 0.01) and 0.5 M + P (P < 0.05) than in 1.5 M sheep. Coronal sections (20 microns) of hypothalamic brain tissue were subjected to in situ hybridisation to determine gene expression for neuropeptide Y (NPY). NPY mRNA was concentrated in the arcuate nucleus and median eminence, with total amounts greater in both 0.5 M (310%, P < 0.001) and 0.5 M + P (333%, P < 0.01) groups than in 1.5 M sheep (100%). These data reveal that chronic low dietary energy intake by long-term castrates, with high or low protein intake, reduces LH pulse frequency but increases the circulating levels of LH by virtue of an increase in pulse amplitude, and concomitantly increases hypothalamic NPY gene expression.

Animals↗
PubMed1996

Central melatonin receptors in red deer (Cervus elaphus).

Red deer display characteristic seasonal changes in appetite, growth, and reproduction which are mediated by the pineal hormone, melatonin, which provides a direct neuroendocrine transduction of the ambient photoperiod. To identify potential central sites of action for this hormone, [2(-125)I]iodomelatonin binding sites were localized and characterized within the cervine brain and pituitary by in vitro autoradiography. Specific binding was distributed over a number of discrete regions of the brain, including the cortex, septum, putamen, hippocampus, cerebellum, and superior colliculus. The choroid plexus, the pars tuberalis, and the pars distalis of the pituitary were also specifically labeled. Specific binding was completely abolished in the presence of 10(-7) M melatonin and inhibited in the presence of 10(-4) M GTP gamma S (guanosine-5-O-(3-thiotriphosphate)), a nonhydrolysable analogue of GTP, in the pars tuberalis, pars distalis, choroid plexus, and all neuronal regions examined apart from the hippocampus and layer III of the cerebral cortex. Inhibition of [2(-125)I]iodomelatonin binding by GTP gamma S is indicative that binding is representative of a G-protein-coupled receptor. Characterization studies showed that [2(-125)I]iodomelatonin binding was time-dependent and saturable with a dissociation constant (Kd) in the low picomolar range (approximately 10 pM). Competition studies with iodomelationin, melatonin, and N-acetylserotonin gave IC50 values similar to those previously characterized for the melatonin receptor in the ovine pars tuberalis.

Animals↗
PubMed1995

Superovulatory responses to eCG in llamas (Lama glama ).

Llamas are copulation-induced single-ovulators, and multiple ovulation and embryo transfer (MOET) methods have not yet been developed for this species. Superovulatory responses to eCG given during an induced (Group A) or simulated (Group B) luteal phase were investigated using ultrasound to observe ovarian follicles and corpora lutea (CLs) and plasma progesterone was used to assess luteal function. Embryos were recovered nonsurgically. Group A (n = 19): donors were given 8 microg, im GnRH analogue (Day 0) to induce ovulation of a mature follicle, 1000 IU, im eCG (Day 7), and 250 microg PGF(2alpha) analogue (Day 9). Group B (n = 17): donors were given a subcutaneous progestagen implant (3 mg Norgestomet) at Days 0 to 7) and 1000 IU, im eCG (Day 5). When most (>65%) of the follicles in both Groups A and B had matured at 5 to 11 d post eCG, the donors were given 8 microg, im GnRH and mated once (n = 26) or twice within a 24-h interval (n = 10); embryos were recovered 6 to 9 d post ovulation. More follicles and corpora lutea were induced in Group B than in Group A, but a similar mean number of embryos were recovered (1.3 vs 1.6), and a similar proportion of donors yielded multiple embryos (35 vs 32%). The embryo recovery rate was similar for Groups A and B (39 and 37%), but it was higher (P < 0.001) with 2 (72%) rather than 1 (22%) mating, and it was negatively correlated with CL number (P < 0.05). Overall, 80% of the llamas had a precocious CL and elevated plasma progesterone concentrations when multiple follicles reached maturity. This was associated with increased subsequent superovulation and embryo recovery (P < 0.01). Peak plasma progesterone was positively correlated with the CL number (P < 0.05). From these results we conclude that superovulation may be achieved with eCG given during either an induced or a simulated luteal phase, that embryo recovery is improved following 2 matings rather than 1, and that MOET may indeed be feasible for use in the llama.

Journal Article↗
PubMed1995

Influence of prenatal photoperiod on postnatal plasma concentrations of progesterone and prolactin in female red deer (Cervus elaphus) reared in constant equatorial photoperiod.

Prenatal photoperiod influences postnatal prolactin secretion and the timing of reproductive development in male red deer reared from birth in a constant equatorial photoperiod (12:12 light:dark). The present trial investigated whether a similar phenomenon occurs in female red deer. Female deer whose mothers had been exposed for the last 14 weeks of gestation to long (group L, 18:6 light:dark) or short day length (group S, 6:18 light:dark) were kept from birth in constant equatorial day length with food available ad libitum. Both groups showed similar live-weight gain to 90-100 weeks of age. Blood samples taken once or twice weekly were analyzed for progesterone and prolactin. Progesterone concentrations indicated that there was no difference between the groups in the timing of the first incidence of ovarian (luteal) activity, which occurred at a normal or late age for natural puberty (67 weeks or older). Only one individual per group exhibited normal repeated luteal cyclicity since there was a high incidence of irregular or abnormal luteal function. Plasma prolactin concentrations at birth were higher in group L than group S (P < 0.001). Thereafter, although the mean and peak values did not differ significantly between the groups, there was a significant difference in the pattern of secretion; deer in group L showed significant clustering of prolactin peaks (P < 0.01) at a mean age of 48 weeks, whereas deer in group S showed a random distribution of peaks. Therefore, for female red deer raised in constant equatorial photoperiod, prenatal long day lengths did not advance timing of puberty.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Influence of prenatal photoperiod on postnatal reproductive development in male red deer (Cervus elaphus).

Male red deer calves, whose mothers had been kept for the last 14 weeks of gestation in long days (18 h light:6 h dark) (group L, n = 7) or short days (6 h light:18 h dark) (group S, n = 5), were kept in constant intermediate daylength (12 h light:12 h dark) from birth to 75 weeks of age. Both groups showed the same live-weight gain. Mean plasma LH concentrations were higher in group L than in group S from birth to 20 weeks of age (averaging 1.55 versus 0.48 ng ml-1, P < 0.001), from 21 to 45 weeks (1.65 versus 1.32 ng ml-1, P < 0.05) and from 46 to 50 weeks (1.84 versus 1.27 ng ml-1, P < 0.001); thereafter, there was no significant difference between the groups (1.81 ng ml-1). Mean concentration of plasma testosterone was relatively low from birth to 30 weeks (averaging 0.38 and 0.27 ng ml-1 (P < 0.05) in groups L and S, respectively), but thereafter increased to a maximum which was greater (2.78 versus 1.46 ng ml-1, P < 0.01), and occurred earlier (47 versus 68 weeks of age, P < 0.001) and at lower body weight (82 versus 96 kg, P < 0.01) in group L compared with group S. Growth of antlers started in both groups at 25 weeks, but they hardened earlier in group L than in group S (42 versus 47 weeks of age, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Ultrasonography as an aid to controlled breeding in the llama (Lama glama).

An ultrasonic linear array scanner with a transrectal probe was used to observe ovarian and uterine changes associated with the reproductive cycle in llamas. 'Waves' of follicular development and regression occurred in unstimulated females, during which the dominant follicle reached a maximum size of 9 to 13 mm; both ovaries were equally active. Ovulation was induced by mating in 80 per cent of cases, and when mating was accompanied by the administration of human chorionic gonadotrophin the ovulation rate increased to 90 per cent and the time to ovulation decreased from two to three days to one to two days. Some spontaneous ovulations occurred. Corpora lutea reached a maximum size of 12 mm (non-pregnant) or 14 mm (pregnant) after seven or 16 days, respectively. The lifespan of the corpus luteum was approximately 11 days in non-pregnant llamas and the regression time was advanced by the administration of prostaglandin or embryo recovery. Pregnancy could be diagnosed as early as 19 days after mating.

Animals↗
PubMed1992

Influence of prenatal photoperiod on postnatal prolactin secretion in red deer (Cervus elaphus).

Plasma prolactin concentrations were higher (P < 0.001) in newborn red deer calves whose mothers had been maintained for the last 14 weeks of gestation in long days (18 h light) (group L, n = 9) than in those whose mothers had been kept over the same period in short days (6 h light) (group S, n = 5). After transfer of all hinds and suckled calves on the day of birth to constant intermediate daylength (12 h light), prolactin concentrations decreased exponentially (P < 0.001) in group L calves, but not in group S, during the first 21 days. Thereafter, prolactin fell to a nadir in group L calves and rose to peak values in group S calves at 8-12 weeks post partum (P = 0.003), before converging again by 14 weeks. The pattern of prolactin secretion over the first 14 weeks of life was therefore significantly affected by prenatal photoperiod. Plasma prolactin concentrations in the adult hinds were higher (P < 0.001) in group L than group S at 4-10 weeks before parturition; they were similarly high around parturition and fell thereafter to baseline values after 7 weeks. These results provide evidence that deer fetuses respond to photoperiodic information, thereby acquiring a photoperiodic history in utero that influences postnatal responses to photoperiod.

Animals↗
PubMed1989

Plasma progesterone concentrations in pregnant and non-pregnant llamas (Lama glama)

Female llamas ovulate in response to copulation, and progesterone secretion by the corpus luteum indicates recent ovulation (mating) and, or, pregnancy. The plasma progesterone concentration was 0.9 to 1.4 ng/ml in five non-pregnant llamas and 7.4 to 9.2 ng/ml in three llamas in the last month of pregnancy. After ovulation had been induced in nine of 10 llamas by a single intramuscular injection of 500 or 750 iu of human chorionic gonadotrophin, the plasma progesterone concentration increased after two days from 0.5 to 1.2 ng/ml to 4.6 to 10.3 ng/ml after six to nine days and returned to basal values after 10 to 13 days, reflecting the life-span of a corpus luteum in the absence of conception. After a male llama had been introduced into a group of 13 females, 10 matings which resulted in eight conceptions occurred in the first 11 days, and 11 of the llamas became pregnant. The llamas' progesterone concentrations increased after mating and remained high if conception had occurred: 6 to 12 ng/ml in months one to four, and 5 to 9 ng/ml in months five to nine of the 11-month gestation. Two of the 13 llamas had high concentrations of progesterone although they did not become pregnant.

Animals↗
PubMed1989

Melatonin can induce year-round ovarian cyclicity in red deer (Cervus elaphus).

From 17 February 1987 (Day 1) to 5 June 1988 (Day 475), 6 red deer hinds which had been in natural daylength (NL/M) and 6 hinds which had been in continuous artificial light for the previous month (CL/M) were each given melatonin (5 mg in feed) daily at 15:00 h. Six controls (C) received unsupplemented feed. From Day 1 all hinds were in natural daylight and ovarian cyclicity was assessed from plasma progesterone concentrations. Group C first went into anoestrus on 15 March 1987 (Day 27 +/- 9.2 (s.e.m], recommenced cyclicity on 23 October (Day 249 +/- 2.3) and went into anoestrus again on 2 April 1988 (Day 411 +/- 8.7). Group CL/M first went into anoestrus 31 days earlier (P less than 0.05) on 12 February (Day -4 +/- 7.8), before the start of melatonin treatment; 4 hinds then recommenced ovarian cycles 132 days earlier (P less than 0.001) on 13 June (Day 117 +/- 5.8) and continued to cycle for a longer period than did controls. Group NL/M hinds were cyclic at the start of melatonin feeding and continued to cycle for 1 year or more (N = 6). Plasma prolactin concentrations remained suppressed (less than 20 ng/ml) for the duration of melatonin-feeding (Groups CL/M and NL/M) whereas control values (Group C) were elevated (20-120 ng/ml) between April and August (P less than 0.05). The ovarian response by hinds to melatonin therefore depends on initial reproductive status and recent photoperiodic history, and continued administration to cyclic hinds stimulates prolonged ovarian cyclicity irrespective of the time of year.

Animals↗