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Biomedical subjects

R W Lea

Publications and source records attributed to R W Lea.

At least 55 records · Page 3Linked to original sources
PubMed1989

Concentrations of plasma prolactin and luteinizing hormone following nest deprivation and renesting in ring doves (Streptopelia risoria).

Ring doves with increased plasma prolactin and low plasma LH (Group A) or with low plasma prolactin and low plasma LH (Group B) which had been incubating sterile eggs for 12 or 18 days, respectively, had their nests and eggs removed for 3 days. Upon nest return, observations were made on the birds' readiness to renest and on changes in plasma prolactin and LH. Birds from Group A demonstrated a far greater tendency to resume incubation than birds from Group B. Nest deprivation resulted in a sharp fall in the concentration of plasma prolactin in birds which were deprived of their nests after 12 days of incubation (Group A). Following resumption of incubation no subsequent increase in the prolactin levels was observed in Group A or B. The concentration of plasma LH rose sharply after nest deprivation in both sexes of both groups and declined after return of the nests. Birds in Groups A and B which returned to their nests laid a new clutch of eggs while continuing to incubate. The total length of uninterrupted sitting following nest return was 20.9 +/- 0.48 days (n = 8). These results suggest that (1) once the mechanism responsible for the increase in plasma prolactin during incubation is disrupted, it cannot be reactivated unless the whole reproductive cycle is repeated. (2) The inhibition of LH secretion during incubation involves neural mechanisms which do not necessarily involve the anti-gonadotrophic action of prolactin.

Animals↗
PubMed1988

Endocrine changes in photostimulated willow ptarmigan (Lagopus lagopus lagopus) and Svalbard ptarmigan (Lagopus mutus hyperboreus).

Changes in plasma luteinizing hormone (LH), testosterone, thyroxine (T4), and triiodothyronine (T3) and the height of supraorbital combs were compared in captive willow ptarmigan (Lagopus lagopus lagopus) and Svalbard ptarmigan (Lagopus mutus hyperboreus) exposed to an artificial annual cycle of daylength simulating that at 70 degrees N. Plasma LH and testosterone and comb height increased more slowly in Svalbard than in willow ptarmigan as daylength increased. In both species, plasma LH and testosterone fell abruptly, and the supraorbital combs regressed in June, marking the development of long-day refractoriness. Comparison with free-living Svalbard ptarmigan (K.-A. Stokkan, P. J. Sharp, and S. Unander (1986) Gen. Comp. Endocrinol. 61, 446-451) at 80 degrees N, showed a similar slow increase in reproductive function before the onset of the breeding season. However, maximum plasma LH levels and comb size were higher in free-living than in captive Svalbard ptarmigan. Furthermore, long-day refractoriness developed earlier in captive than in free-living Svalbard ptarmigan. In both species of ptarmigan, the development of long-day refractoriness was associated with increased plasma prolactin. This increase was larger and occurred earlier in the Svalbard than in the willow ptarmigan. Seasonal changes in thyroid hormones were not as marked as for the other hormones measured. In both species, plasma T4 tended to increase and plasma T3 to decrease as daylength increased. A small increase in plasma T3 was seen after the development of long-day refractoriness in both species. It is concluded that captivity depresses the photoperiodic response of Svalbard ptarmigan more than that of willow ptarmigan.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Reductions in plasma LH concentration and testicular weight in ring doves following intracranial injection of prolactin or growth hormone.

Testicular weights and concentrations of LH in plasma were measured in individually housed adult male ring doves given five daily intracerebroventricular injections of saline-NaHCO3 vehicle (2 microliter), ovine prolactin (0.1, 0.5, 1.0 or 2.0 micrograms/day), turkey prolactin (1.0 micrograms/day), turkey GH (1.0 micrograms/day) or ovine GH (1.0 micrograms/day). Administration of ovine prolactin resulted in a dose-dependent suppression of plasma LH concentration, with values in the two highest dose groups averaging three- to fivefold less than those of vehicle-injected controls. Reductions of similar magnitude were obtained following intracranial administration of turkey, ovine or human GH. Whilst effective in reducing plasma LH, turkey prolactin was less effective than an equivalent dose of ovine prolactin. Testicular regression was observed in all treatment groups which showed a significant decrease in plasma LH concentrations. Because crop sacs remained undeveloped in all treatment groups, it was concluded that these centrally administered hormones acted primarily at the level of the brain or pituitary to exert their suppressive effects. The possibility that prolactin and GH interact with different binding sites to inhibit LH secretion is discussed, together with evidence for a possible role of prolactin and GH in gonadotrophin regulation under normal physiological conditions.

Animals↗
PubMed1988

Relationships between prolactin, LH and broody behaviour in bantam hens.

The interactions between broody behaviour and changes in concentrations of plasma prolactin and LH were investigated in bantam hens. Adoption of newly hatched chicks caused incubating hens to leave their nests and prevented plasma prolactin decreasing as rapidly as in hens deprived of their nests and not given chicks. Further, the hens allowed to rear chicks came back into lay later (P less than 0.001) than the hens not allowed chicks. Plasma prolactin decreased and plasma LH increased in hens deprived of their nests: these changes were reversed when the hens re-nested. The changes in plasma LH and prolactin in nest-deprived and re-nesting birds were not always synchronous; this was particularly clear immediately after nest deprivation when the increase in plasma LH preceded the decrease in the plasma prolactin. Readiness to incubate disappeared between 48 and 72 h after nest deprivation and corresponded with the time when plasma prolactin decreased to baseline values. Administration of ovine prolactin depressed (P less than 0.01) the initial increase in plasma LH after nest deprivation, but repeated administration of prolactin for up to 72 h failed to suppress plasma LH to the values found in incubating hens. Repeated administration of ovine prolactin at 5- to 8-h intervals for 72 h maintained readiness to incubate in nest-deprived hens. It is concluded that the secretion of prolactin in broody hens is facilitated by the presence of chicks and that increased concentrations of plasma prolactin maintain incubation behaviour. In incubating hens the secretion of LH and prolactin may be partly regulated independently. In addition, LH secretion may also be inhibited by increased plasma prolactin.

Animals↗
PubMed1987

Daily variations in monoamine turnover in the brain of the ring dove (Streptopelia risoria).

A method for measuring the concentration and turnover of serotonin, dopamine and noradrenaline in small amounts of brain tissue was validated for the ring dove (Streptopelia risoria). Turnover rates of the catecholamines calculated as the rate of depletion after tyrosine hydroxylase inhibition agreed well with turnover rate measured as rate of accumulation after inhibition of monoamine oxidase at 2.5 h, but not 5 h, after drug administration. Using the monoamine oxidase inhibitor, pargyline, turnover of serotonin, dopamine and noradrenaline were estimated in the same tissue. Both the concentration and turnover of the amines in hypothalamus, paleostriatum and hyperstriatum fluctuated over a 24 h period. Serotonin turnover was greatest during the middle of the dark period in all three tissues. In contrast, for both dopamine and noradrenaline the highest turnover was observed during the light period and the lowest during the dark period.

Animals↗
PubMed1986

Vasoactive intestinal polypeptide stimulates prolactin release in vivo in the ring dove (Streptopelia risoria).

I.v. administration of vasoactive intestinal polypeptide (VIP) to ring doves significantly elevated the plasma concentration of prolactin after 10 min in a dose-related manner. The plasma prolactin concentration of nonbreeding doves with low basal levels was increased by a similar amount as in brooding doves whose initially high concentration of plasma prolactin had been reduced by nest deprivation prior to treatment.

Animals↗
PubMed1986

Evidence that vasoactive intestinal polypeptide is a physiological prolactin-releasing factor in the bantam hen.

Vasoactive intestinal polypeptide (VIP)-like material was localised immunohistochemically in the hypothalamus of the bantam hen. Abundant immunoreactive VIP terminals were seen in the external layer of the median eminence and most immunoreactive VIP cell bodies were located in the basal hypothalamus. A few immunoreactive VIP cell bodies and many fibres were found in the preoptic hypothalamus. Intravenous injections of synthetic porcine VIP over a dose range of 12.5 to 100 micrograms kg-1 body wt resulted in dose-related increase in concentration of plasma prolactin in incubating bantams deprived of their nests for 24 hr. These doses of VIP did not stimulate the release of growth hormone. Studies in vitro showed that synthetic VIP directly stimulated prolactin release from the anterior pituitary gland. The glands from incubating bantams were more responsive to the prolactin-releasing effects of VIP than were the glands from laying birds. Studies in vitro showed that the amount of prolactin released in response to an iv injection of 50 micrograms kg-1 VIP was greater in incubating birds deprived of their nests for 24 hr than in laying hens. Prolactin release was not stimulated in ovariectomized hens after an injection of 50 micrograms kg-1 VIP unless the birds were first treated with oestrogen or oestrogen and progesterone. It was concluded that a VIP-like material in the bantam hypothalamus may be a physiological prolactin-releasing factor acting at least in part at the level of the anterior pituitary gland.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

External factors affecting the duration of broody behavior in the ring dove (Streptopelia risoria).

The object of this study was to investigate factors which determine the duration of sitting in ring doves. This normally lasts ca. 19 days from laying, with very small variation. The period is made up of 15 days incubating eggs and 4-5 days brooding squabs. The duration of sitting is unaffected by substituting fresh or sterile eggs, and can only be slightly influenced by substituting foster squabs or new eggs just before or after hatching. The sitting period appears to be predetermined to run for 19 days following laying. The maintenance of sitting, however, requires the presence of the nest and eggs, and can be drastically varied by keeping subjects in continuous daylight or on a day of 6 hr light:6 hr dark (6 L:6 D). Birds kept on ahemeral cycles (11 L: 10 D; 13 L:14 D) displayed significantly different periods of incubation on infertile eggs and recycling, indicative of an endogenous circadian basis to the timing mechanism.

Animals↗
PubMed1986

Changes in aromatase activity in the brain of the male ring dove (Streptopelia risoria) during the breeding cycle.

Aromatase activity was measured in striatal and hypothalamic regions of the brain of the male ring dove throughout its breeding cycle. The enzyme activity in the anterior hypothalamus and hyperstriatum was significantly reduced in broody birds. A reduction in plasma LH and the number of spermatogonia per tubule cross-section were also observed at this time. The results support the view that testosterone is involved in the control of aromatase activity in the anterior hypothalamus and hyperstriatum. The enzyme activity in the posterior hypothalamus, paleostriatum and archistriatum showed no changes throughout the breeding cycle, indicating that other factors in addition to testosterone are involved in controlling the enzyme in these tissues.

Animals↗
PubMed1986

Seasonal changes in concentrations of plasma hormones in the male ring dove (Streptopelia risoria).

Seasonal changes in concentrations of plasma LH, prolactin, thyroxine (T4), GH and corticosterone were measured in captive male ring doves exposed to natural lighting at latitude 56 degrees N. Plasma LH levels decreased steeply in autumn when the daylength fell below about 12.5 h but increased in November as the birds became short-day refractory. In comparison with plasma LH concentrations in a group of short-day refractory birds exposed to 6 h light/day from the winter solstice, plasma LH levels in birds exposed to natural lighting increased further in spring after the natural daylength reached about 12.5 h. There were no seasonal changes in plasma prolactin concentrations and plasma T4 concentrations were at their highest during December, January and February, the coldest months of the year. The seasonal fall in plasma LH levels in September was associated with a transitory increase in plasma T4, a transitory decrease in plasma corticosterone and a sustained increase in plasma GH. It is suggested that in the ring dove, short-day refractoriness develops rapidly in November to allow the bird to breed when the opportunity arises, during the winter and early spring. The annual breeding cycle is synchronized by a short-day induced regression of the reproductive system in the autumn, the primary function of which may be to enable the birds to meet the energy requirements for the annual moult. The changes in plasma T4, corticosterone and especially of GH at this time of year are probably concerned with the control of moult or the associated changes in energy requirements.

Animals↗
PubMed1986

Factors affecting prolactin secretion during the breeding cycle of the ring dove (Streptopelia risoria) and its possible role in incubation.

Plasma prolactin began to increase significantly about 5 days after the onset of incubation in both sexes of the dove to reach a peak at the time of hatch. At this time, the concentration of prolactin in the plasma of the female was significantly higher than in the male. In the middle of the incubation period prolactin levels measured over a 24-h period remained constant in both sexes, although the male sits during the middle of the day and the female for the rest of the time. Nest deprivation resulted in a sharp, significant decline in the concentration of prolactin in both sexes. Newly hatched squabs stimulated the release of prolactin only in those doves which had been incubating eggs for several days. A distinct sex difference was observed in the expression of nest defence behaviour of the ring dove during the breeding cycle. At the time of laying, the female was significantly more aggressive than the male and her aggression increased only slightly up to the time of hatching. In contrast, male aggression increased gradually from a low level at laying to reach a peak at the time of hatching. The levels of plasma progesterone in the female showed a significant increase around the time of lay. No significant changes occurred in the plasma concentration of either progesterone or 17 alpha-hydroxyprogesterone in the male. Administration of prolactin increased the length of time of incubation of infertile eggs. Nest manipulations which had the effect of inducing the doves to begin incubation 4 days before laying showed that (1) the length of time of incubation of infertile eggs is fixed and independent of events which occur at courtship or oviposition, (2) the initiation of the increase in plasma prolactin concentration during incubation is independent of events which occur at courtship and oviposition and (3) the termination of incubation is always preceded by a fall in the concentration of plasma prolactin. It is concluded that the length of time of incubation is dependent upon sustained raised levels of plasma prolactin. The concentration of plasma prolactin increases several days after the onset of incubation in response to the tactile stimulation of sitting. High levels, if maintained by visual stimulation from the nest, maintain incubation for a fixed period. After this, if the eggs fail to hatch, prolactin levels fall and the doves cease incubation and begin a new cycle.

Animals↗
PubMed1985

Biochemistry and physiology of monoamine oxidase (MAO) activity in the ring dove (Streptopelia risoria). I. Characteristics of MAO activity in vitro.

Monoamine oxidase (MAO) activity was measured in ring dove (Streptopelia risoria) tissues using a fluorometric assay with kynuramine as substrate. Harmaline inhibited MAO activity in a time-dependent manner, and preincubation of enzyme with the drug did not affect its activity. Pargyline produced a slow-onsetting inhibition of activity which was enhanced by preincubation of enzyme and inhibitor. Harmaline displayed reversible non-competitive inhibition of MAO activity. Oxygen is also a substrate for dove MAO, and the reaction apparently involves "ping-pong", double-displacement kinetics. Dove MAO activity is temperature-dependent, with an activation energy of 13.1 kcal/mole.

Animals↗
PubMed1985

Biochemistry and physiology of monoamine oxidase (MAO) activity in the ring dove (Streptopelia risoria). II. Distribution of MAO in different tissues.

Monoamine oxidase (MAO) activity was measured fluorometrically in liver, kidney, intestine and brain of adult male and female ring doves. Liver MAO was inhibited in a concentration-related fashion by clorgyline and harmaline (MAO type A inhibitors) where a plateau in the inhibition curve occurred with about 15% activity remaining, and also by the type B inhibitor deprenyl, which produced a plateau when about 85% activity remained. Kidney, intestine and brain MAO were inhibited in a biphasic manner by harmaline. Results with inhibitors suggest that 85% of liver MAO, 86% of kidney MAO, 88% of intestine and 75% of brain MAO is type A. Using 10(-6) M harmaline to differentiate between MAO-A and MAO-B type activities, the apparent maximal velocities (Vmax) and Michaelis constants (Km) were determined in different tissues. Most activity occurred in the intestine, with proportionally lesser amounts of kidney, liver and brain. The majority of MAO present was in the A form. Except for kidney, Km of MAO-B was higher than that of MAO-A. Both MAO-A and -B activities were higher in the intestines of male birds, although sex differences in content and type of MAO activity were not observed in other tissues of the ring dove.

Animals↗
PubMed1984

Plasma concentrations of luteinising hormone, follicle stimulating hormone, androgen, growth hormone, prolactin, thyroxine and triiodothyronine during growth and sexual development in the cockerel.

Changes in concentrations of plasma luteinising hormone (LH), follicle stimulating hormone (FSH), androgen, growth hormone (GH), prolactin (Prl), thyroxine (T4) and triiodothyronine (T3) were measured during growth and sexual maturation in broiler cockerels reared in continuous light to 7 weeks and 14 h light/d thereafter. Concentrations of LH and FSH began to increase between 13 and 15 weeks, while those of androgens increased between 16 and 17 weeks. FSH concentration increased faster than that of LH. Concentrations of GH and Prl were high at 3 weeks; that of GH decreasing progressively between 3 and 14 weeks of age and thereafter remaining low, while that of Prl was low between 5 and 9 weeks, relatively high between 10 and 13 weeks, and then temporarily decreasing before increasing progressively during sexual maturation. Concentrations of T3 and T4 were higher in juvenile than in adult birds.

Androgens↗
PubMed1984

Influence of lighting cycles on daily rhythms in concentrations of plasma tri-iodothyronine and thyroxine in intact and pinealectomized immature broiler hens (Gallus domesticus).

The effects of pinealectomy on the daily rhythms of concentrations of tri-iodothyronine (T3) and thyroxine (T4) were investigated in sexually immature female chickens exposed to 21-, 24- and 27-h cycles of light and darkness, or to extended periods of light or darkness for more than 24 h. In pinealectomized and control birds, rhythms in levels of plasma T3 and T4 were entrained by all lighting cycles and decreased in amplitude or disappeared in continuous light or darkness. In pinealectomized and control birds held on 21-h (11 h light:10 h darkness; 11L:10D) and 24-h (14L:10D) lighting cycles, the peak of the T4 rhythm coincided with, or lagged, the trough in the rhythm of T3 while in birds held on a 27-h (14L:13D) lighting cycle, the peak of the T4 rhythm preceded the trough in the rhythm of T3. Pinealectomy resulted in significant effects on the phases or amplitudes of rhythms of T3 or T4 in all lighting schedules except 4L:20D. However, these effects were not consistent in direction between experimental groups and were, therefore, of doubtful physiological significance. Pinealectomy increased the mean level of plasma T4 in birds exposed to continuous light or darkness or to 4L:20D. A corresponding reduction in mean levels of plasma T3 was seen in birds exposed to continuous light or darkness. It is concluded that under the lighting conditions investigated pinealectomy had no clear effect on the phases or amplitude of daily rhythms of levels of T4 or T3. However, after the effects of the feeding pattern on thyroid hormone rhythms imposed by the lighting cycle were removed by placing birds in constant lighting conditions, pinealectomy appeared to exert an inhibitory action on thyroid function.

Animals↗
PubMed1982

Plasma prolactin concentrations in broody turkeys: lack of agreement between homologous chicken and turkey prolactin radioimmunoassays.

1. Plasma concentrations of prolactin, measured using homologous chicken or turkey prolactin radioimmunoassays, increased 2- and 9-fold, respectively in somatically mature turkey hens transferred from short (6 h light (L): 18 h dark (D)) to long (14 L:10 D) photoperiods. 2. A further increase in plasma prolactin was observed in laying hens 2 to 3 weeks before the onset of incubation. This increase was detected using the turkey prolactin assay but not the chicken prolactin assay. 3. The onset of incubation was not always associated with the cessation of egg production. Egg laying stopped in incubating hens only after plasma concentrations of prolactin were approaching their maximal values. These were 10-fold higher than the prolactin concentrations at the onset of lay. 4. The removal of clutches of eggs from incubating hens resulted in a decrease in plasma concentrations of prolactin, which was associated with the cessation of incubation in two hens which had been incubating for 52 and 47 d. The decrease was only temporary in two hens which had been incubating for 8 and 32 d. The latter two hens continued to show incubation behaviour although they were not sitting on eggs. 5. In four turkey hens which did not become broody, egg production ceased after 12 weeks exposure to 14 L:10 D. The concentration of plasma prolactin, as measured using the turkey prolactin assay, increased 2-fold during the 2 weeks before these hens stopped laying.

Animals↗