Biomedical subjects

N B Carter

Publications and source records attributed to N B Carter.

10 recordsLinked to original sources

PubMed1991

Effects of prolonged artificial photoperiod on circulating prolactin and melatonin levels in seasonal ewes.

Crossbred ewes exposed to long days for 46 months prior to photoperiod reversal showed no alteration in the duration or amplitude of the circulating melatonin peak between 24 and 46 months of continuous long day exposure. By 3 months after photoreversal to short days, both the amplitude and duration of the peak had adapted to the new scotophase. In short day treated ewes, the melatonin peak was abolished by 46 but not 24 months of short day exposure, and was not fully restored in all ewes 3 months after photoreversal. Mean prolactin levels over 24 h remained high up to 46 months of long day treatment, and declined 3 months after short day exposure. Conversely, mean prolactin levels remained low up to 46 months of short day treatment, increasing 3 months after exposure to long days. Thus: (i) depletion of the melatonin-synthesizing capability of the ovine pineal gland by prolonged exposure to long nights is not completely reversed after 3 months of continuous long day exposure, and (ii) a nocturnal melatonin peak is not essential for maintenance of plasma prolactin levels under these conditions.

Animals↗

PubMed1991

Plasma concentrations of luteinising hormone and body weights during somatic maturation in intact and castrated Australorp cockerels from a line of hens selected for increased ovulation rate.

1. Plasma concentrations of luteinising hormone (LH), comb size and body weight were measured between 46 and 208 d of age in intact and castrated cockerels from lines of selected and control Australorp domestic chickens. The selected line had been selected for increased rate of lay by reducing oviposition intervals within sequences. The cockerels were reared and maintained on 15.25 h light/d. 2. Concentrations of plasma LH in the intact control cockerels were low in the 'immature' phase (less than 100 d old) and increased during the 'mature' phase (older than 175 d) with a peak occurring when the testes are beginning to grow at the onset of the 'mature' phase. In comparison with the control line of cockerels, the selected line had significantly higher plasma LH concentrations at the onset of the 'mature' phase. Selection had no effect on the mean concentration of plasma LH in either the immature phase or a few weeks after the onset of the mature phase. 3. There was no effect of selection in sibling females for higher rates of lay on changes in comb size or body weight during sexual maturation in the intact cockerels. 4. Castration at 45-46 d of age resulted in increased plasma LH concentrations and no comb growth. Plasma LH concentration increased progressively between 40-208 d. There was no difference between the two lines of cockerels in plasma LH concentration or rate of body growth after castration. 5. It is concluded that selection of females for a change in the rate of egg production has resulted in increased plasma LH concentrations in sibling males around the onset of sexual maturation. Selection appears to have caused this effect by altering an unidentified component of the inhibitory feedback mechanism which controls the tonic secretion of LH.

Animals↗

PubMed1989

Seasonal modification of ovine pineal function. I. Interaction of gonadal steroids and sympathetic innervation on beta-adrenoceptors.

The results of a seasonal study of the regulation by steroids of ovine pineal beta-adrenoceptors are reported. The effects of ovariectomy, steroid implants and superior cervical ganglionectomy were investigated in Merino ewes. The results confirm earlier observations showing a seasonal variation in the sensitivity of the receptors to modification by gonadal steroids. A marked difference in receptor density and affinity between the follicular and luteal phases of the estrous cycle is shown for the first time, a difference which can be modified by appropriate steroid-related treatments. A season-dependent antagonism between the sympathetic innervation of the gland (presumably acting via the neurotransmitter noradrenaline) and gonadal steroids in the regulation of ovine pineal beta-adrenoceptor function is also shown.

Animals↗

PubMed1989

Seasonal modification of ovine pineal function. 2. Steroidal effects on melatonin and prolactin profiles.

Pineal beta-adrenoceptor density and affinity in ewes are modified in a season-dependent manner by gonadal steroids and by the sympathetic innervation of the gland. The present study was undertaken to relate the steroidal effects on the receptors to post receptor endocrine events, and to investigate the influence of the sympathetic innervation of the pineal gland on these events. Plasma melatonin and prolactin profiles were determined during anestrus and during the normal breeding season in ewes subjected to sympathetic denervation of the pineal and/or a range of steroid-related treatments. Wherever valid comparisons could be drawn between effects of the treatments on beta-adrenoceptor variables and on circulating hormone levels, similar effects were noted. Further, ganglionectomy influenced hormone profiles similarly to estradiol under all conditions tested. It appears that gonadal steroids (estradiol) and the sympathetic neurotransmitter noradrenaline have opposing actions on prolactin levels, just as they have on pineal beta-adrenoceptor binding affinity. These findings suggest that steroid-mediated changes in receptor number and affinity are reflected in post receptor endocrine events. In addition, other factors (e.g. photoperiodic information transmitted via the sympathetic innervation) also play important roles in the regulation of the observed hormonal profiles. A steroid-mediated feedback regulation of pituitary prolactin release, partly direct and partly via pineal melatonin release, is suggested.

Anestrus↗

PubMed1988

Circulatory effects of a depilatory dose of mouse epidermal growth factor in sheep.

1. Haemodynamic parameters and tissue blood flow rates were measured in two groups of five sheep infused I.V. for 24 h with either saline or 128.6 micrograms mouse epidermal growth factor (mEGF) kg-1 body weight. Measurements were made preinfusion and at +3, +12, +24, +27 and +48 h. We wished to assess relationships between blood flow rates and known functional changes in various organs during EGF treatment, especially any relationship between skin blood flow rate and the known depilatory effects of the protein in sheep. 2. Cardiac output increased and total peripheral resistance and mean arterial pressure decreased during and after infusion in the mEGF-treated group relative to the control group. 3. The greatest increase in blood flow rates occurred in woolled skin (+500%) during mEGF infusion, a result which in itself may have been disparate with the known depilatory effects of EGF. The mucosas of the alimentary tract (except abomasum) and the submaxillary and sublingual salivary glands also showed vasodilatation. 4. There were short-term increases in pituitary and adrenal gland blood flow that may have been associated with the corticotrophin-releasing factor properties of EGF. Flow in the thyroids showed the greatest increase post-infusion when thyroid hormone metabolism may have been reverting to normal. Blood flow rates decreased in the pancreas and perirenal fat. 5. Our general conclusion was that mEGF had specific vasodilator effects in the skin, the thyroid, submaxillary and sublingual glands and the mucosas of most of the alimentary tract.

Animals↗

PubMed1988

AIMS ratings--repeatability.

In the present study, two raters, a psychologist and a nurse, each made five independent ratings of 30 different video-recorded patient-examinations. Having thus excluded patient fluctuation, individual-rater consistency and between-rater agreement over the 6 weeks of the study are examined. While between-rater agreement was apparently being maintained, mean AIMS scores steadily increased. In the hands of these raters, AIMS items 2 and 4 emerged as very reliable, while items 1, 6, and 7 showed high variability. Some patients appeared to be hard to rate. Differences between the study raters and the author JB highlight the issue: how reproducible is an AIMS rating?

Dyskinesia, Drug-Induced↗

PubMed1987

Comparisons of time intervals and plasma LH concentrations during the ovulatory cycle of broiler breeder hens maintained under either a 24 h light:dark cycle or continuous light.

The possibility that egg production in broiler breeder hens may be increased by selection for reduced oviposition interval under continuous light was investigated by comparing the pattern of pre-ovulatory releases of plasma luteinising hormone (LH) and the associated ovipositions in the same broiler hens maintained under normal cycles (15.25 h light/d) or continuous light. The lighting conditions had no effect on plasma concentrations of LH before and at the pre-ovulatory LH peak in first, mid-sequence or terminal ovulatory cycles. Plasma LH concentrations were similar during first, mid-sequence and terminal ovulatory cycles. Mid-sequence oviposition intervals and the interval between a mid-sequence LH peak and its associated oviposition were longer under continuous light than under normal lighting. Pre-ovulatory releases of LH occurred during a restricted period of day in both lighting conditions. Under continuous lighting they were probably entrained by the daily pattern of restricted feeding. Any selection programme for reduced oviposition interval under continuous lighting in broiler breeder hens should take into account the entraining effects of the daily pattern of feeding.

Animals↗

PubMed1986

Plasma concentrations of luteinising hormone during the ovulatory cycle in hens selected for reduced oviposition interval and maintained in continuous light or a 24 h light:dark cycle.

Plasma luteinising hormone (LH) concentrations were measured during the ovulatory cycle in lines of Australorps and White Leghorns selected for reduced oviposition interval and maintained under continuous light and noise. Selection significantly increased plasma LH concentrations in mid-sequence ovulatory cycles of Australorps but not in the White Leg-horns. Selection in the Australorps apparently increased the rate of ovarian follicular maturation, resulting in more frequent LH peaks. The effect of selection on plasma LH concentrations is a function of the lighting condition to which the hens are exposed.

Animals↗

PubMed1985

Effects of selection for reduced oviposition interval on plasma concentrations of luteinising hormone during the ovulatory cycle in hens on a 24 h lighting cycle.

The effects of selection under continuous light for reduced oviposition interval within a sequence of eggs on plasma luteinising hormone (LH) concentrations during the ovulatory cycle were investigated in lines of Australorps and White Leghorns maintained on a 24-h light:dark cycle. Selection did not significantly alter LH concentrations during mid-sequence cycles in either breed. In the control lines, concentrations were higher in the Australorps than in the White Leghorns before and at peak in mid-sequence cycles. The increase in egg production resulting from selection was associated with an advance in the mean time of lay of mid-sequence eggs in both breeds and, in the Australorps, with more pre-ovulatory LH peaks being initiated at the beginning of the open period of the ovulatory cycle. Selection reduced the time an egg spends in the oviduct and, in the Australorps, significantly reduced the interval between a pre-ovulatory LH peak and the oviposition of the egg currently in the shell gland. We suggest that selection under continuous light for reduced oviposition interval increased the rate of ovarian follicular maturation by a mechanism which did not involve an increase in pre-ovulatory concentration of plasma LH in a 24-h light-dark cycle.

Animals↗

PubMed1985

Epidermal hyperplasia and wool follicle regression in sheep infused with epidermal growth factor.

The proliferative activities of germinative cells of the wool follicles and the epidermis have been determined in sheep treated with epidermal growth factor (EGF). Infusions of 0.17-0.72 mg EGF/kg metabolic body weight (MBW) for 28 h resulted in marked declines in the mitotic indices (MI) of the follicle bulb cell populations 24 h after the beginning of treatment, the lowest values being recorded at 48 h. Follicular activity subsequently recovered and the MI returned to preinfusion levels after 3-8 days. The inhibition of fiber production resulting from the decline in bulb cell division caused the development of a break in the fleece. By contrast, the MI of the peripheral cells of the sebaceous gland acini and the basal cells of the epidermis increased after EGF treatment, reaching peaks 48-72 h after the beginning of infusion. The degree to which all of these responses were observed appeared to be approximately correlated with the amount of EGF administered.

Animals↗