Biomedical subjects

H A Tucker

Publications and source records attributed to H A Tucker.

At least 19 recordsLinked to original sources

PubMed1992

Androgens modulate growth hormone-releasing factor-induced GH release from bovine anterior pituitary cells in static culture.

Static primary cultures of bovine anterior pituitary (AP) cells were utilized to study the effect of sex steroids on basal growth hormone (GH) and GH-releasing hormone (GRF)-stimulated release of GH. The AP cells (5 x 10(5) cells/well) were allowed to attach for 72 hr and become confluent before treatments were imposed. Cells were incubated for an additional 24, 48 or 72 hr with either estradiol-17 beta (E2, 10(-11) to 10(-8) M), testosterone (T, 10(-8) to 10(-5) M), dihydrotestosterone (DHT, 10(-9) to 10(-6) M) or 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol, 10(-11) to 10(-8) M). Media were collected every 24 hr and GH concentrations determined by RIA. Incubation of calf AP cells with gonadal steroids did not affect (P > 0.05) basal GH released at 24, 48, or 72 hr. In another experiment, calf AP cells were incubated with the same concentrations of the steroids for 24 hr, media harvested, cells washed and challenged in serum-free media for 1 hr with bovine GRF 1-44-NH2 (10(-8) M). In non-steroid treated wells, GRF increased (P < 0.05) GH from 58 to 134 ng/ml. Incubation with E2 or 3 alpha-diol did not affect (P > 0.05) GRF-induced GH release; however, preincubation with T (10(-5) M) and DHT (10(-9), 10(-8) and 10(-7) M) increased (P < 0.05) GRF-induced GH release above control concentrations (195, 235, 190 and 185 ng/ml, respectively). At the doses tested, sex steroids did not affect basal release of GH, but androgens increased responsiveness of somatotropes to GRF.

Amphotericin B↗

PubMed1992

Prolonged suppression of serum concentrations of melatonin in prepubertal heifers.

Our objective was to suppress the daily surge of melatonin in serum of prepubertal dairy heifers by manipulating intensity of light (Experiment 1) and duration of exposure to light (Experiment 2). Heifers in Experiment 1 were exposed to either 12 hr of darkness (000 lux, control), or 400, 800, or 1,200 lux of light during the last 6 hr of their usual 12-hr nocturnal period. During this 6-hr exposure to various intensities of light, melatonin concentrations were similar to their respective daytime baseline values measured under 400 lux of light, but were 62% to 82% lower than melatonin concentrations during their nocturnal surge period. Suppression of melatonin concentrations was similar between 400 and 1,200 lux of light. In Experiment 2, heifers were exposed to LD 8:16, LD 16:8, LD 20:4, or LD 24:0 photoperiods (1,200 lux) for 4 months. Throughout treatment, concentrations and durations of the melatonin surge were suppressed in the LD 24:0 group and were greatest (during the nocturnal period) in the LD 8:16 group. Concentrations of prolactin in serum were elevated in animals under long days relative to LD 8:16 treatment and respective pretreatment periods. In conclusion, continuous light at an intensity of 1,200 lux suppressed the nocturnal surge of melatonin, but increased secretion of prolactin for at least 4 months in prepubertal heifers.

Animals↗

PubMed1991

Melatonin suppression of mammary growth in heifers.

The objective of this study was to determine if melatonin fed in the middle of a long day (16L:8D) reduces mammary parenchymal growth and reduces serum prolactin in prepubertal heifers, thereby mimicking the effects of a short photoperiod. Sixteen prepubertal Holstein heifers were maintained under natural May to August environmental conditions of Michigan plus supplemental lighting to provide a photoperiod of 16L:8D (lights-on 0600-2200 h). At the midpoint of each day, 8 animals were individually fed melatonin (4 mg/100 kg body weight) and 8 were individually fed vehicle (95% ethanol) in 200 g of a grain concentrate mixture. Blood samples were collected at 1-h intervals for 25 h beginning on Day 67. On Day 70 or 72 heifers were slaughtered. No differences were found in body weight gain between melatonin- and vehicle-fed animals. Parenchyma of mammary glands from melatonin-fed heifers had a lower content (24%) and concentration (17%) of deoxyribonucleic acid but a greater concentration of triglyceride (24%) than that of controls. Mean serum prolactin concentration was 27% lower in melatonin-fed animals. In both groups, serum concentrations of prolactin varied throughout the day, with greatest values occurring between 1100 and 1800 h in positive association with changes in ambient temperature. We conclude that melatonin orally administered to prepubertal heifers reduced mammary parenchymal growth and concentration of prolactin in serum. The data support the hypothesis that melatonin mimics photoperiodic effects on mammary growth and prolactin secretion in cattle.

Administration, Oral↗

PubMed1991

Effects of photoperiod on lactotrophs and on dopaminergic and 5-hydroxytryptaminergic neurones in bull calves.

This study was conducted to determine whether photoperiod-induced changes in serum concentrations of prolactin in cattle were associated with changes in activity of dopamine or 5-hydroxytryptamine (5-HT) neurones in the infundibulum/pituitary stalk and the secretion rate and number of lactotrophs in the anterior pituitary gland. Sixteen prepubertal bull calves (approximately 8 weeks of age) were divided into two groups. One group of eight was maintained on a photoperiod of 8 h light: 16 h darkness (8L:16D) and the other group was exposed to 16L:8D for 4 weeks. At this time calves were injected with a decarboxylase inhibitor (m-hydroxybenzylhydrazine dihydrochloride, NSD 1015) which blocks the conversion of dihydroxyphenylalanine (DOPA) to dopamine and of 5-hydroxytryptophan (5-HTP) to 5-HT. Calves were killed with pentobarbital 15 min later. Accumulations of DOPA and 5-HTP in selected brain regions were used as indices of activity of dopamine and 5-HT neurones respectively. Secretory rate and number of prolactin-secreting lactotrophs were determined by reverse haemolytic plaque assay. Relative to calves exposed to 8L:16D, exposure to 16L:8D increased serum concentrations of prolactin by eightfold, anterior pituitary gland weight by 23%, release of prolactin from pituitary explants by 57% and the area of the plaque for prolactin-secreting lactotrophs by 70%. There was no difference in the rates of accumulation of DOPA and 5-HTP in the infundibulum/pituitary stalk of animals exposed to 4 weeks of 16L:8D or 8L:16D.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Effects of increased dietary energy and protein during late gestation on mammary development in gilts.

Thirty-two gilts were used to evaluate the effects of increased dietary energy and CP during late gestation on mammary development. On d 75 of gestation, gilts were assigned randomly in a 2 x 2 factorial arrangement to adequate (5.76 Mcal ME/d) or increased (10.5 Mcal ME/d) energy and adequate (216 g CP/d) or increased (330 g CP/d) protein. On d 105 of gestation, gilts were slaughtered and total mastectomies were performed. Mammary tissue was separated into mammary parenchymal and mammary extraparenchymal stromal tissue and analyzed for DNA, RNA, protein and lipid. No interactions between dietary energy and protein level were detected (P greater than .20). When adjusted for number of mammary glands and maternal BW (weight of the sow less the weight of the fetuses), mammary parenchymal weight was 27% greater (P less than .03) in gilts fed adequate energy than in gilts fed increased energy, but mammary extraparenchymal stroma weight was unaffected by dietary energy level. Total mammary parenchymal DNA was 30% greater in gilts fed adequate energy than in gilts fed increased energy (P less than .03). Total mammary parenchymal RNA (P less than .02) and total mammary parenchymal protein (P less than .02) also were greater in gilts fed adequate energy than in gilts fed increased energy. Dietary protein level did not affect mammary variables measured, except that increased dietary protein tended to reduce mammary extraparenchymal stromal weight (P less than .09). Increased dietary protein between d 75 and d 105 of gestation did not benefit mammary development, but increased dietary energy was detrimental to development of mammary secretory tissue.

Animals↗

PubMed1991

Effects of photoperiod on mammary development and concentration of hormones in serum of pregnant dairy heifers.

Beginning at 128 d of pregnancy, Holstein heifers were exposed to 16 h light, 8 h dark (long days; n = 10) or 8 h light, 16 h dark (short days; n = 10) until 35 d before calving when they were killed. Photoperiod had no effect on weight or proportion of extraparenchymal fat or parenchyma in the mammary gland or on amount of fat, DNA, or RNA in mammary parenchyma. Serum prolactin concentration was 1.7-fold greater under long than under short days. Concentration of melatonin in serum was 2.4-fold greater during dark than light periods. Duration of elevated serum melatonin concentration in the dark period was longer in heifers given short days, but magnitude of this increase was lower than that in heifers exposed to long days. In a second experiment, peak amplitude and area of the periparturient surge of serum concentration of prolactin were 1.8-fold and 1.7-fold greater, respectively, in six Holstein heifers exposed to long days than in six heifers exposed to short days. We conclude that photoperiod had no effect on mammary development during pregnancy, but relative to short days, long days increased serum concentration of prolactin during pregnancy, including the period of the periparturient surge of prolactin.

Animals↗

PubMed1991

Comparison of somatotropin and growth hormone-releasing factor on milk yield, serum hormones, and energy status.

Holstein cows received 12 mg/d of growth hormone-releasing factor (continuous i.v. infusion, n = 5), 14 mg/d of bST (single daily i.m. injection, n = 8), or no treatment (controls, n = 8) for 60 d. Compared with controls (31.6 kg/d), bST and growth hormone-releasing factor increased milk yield to 34.2 and 37.0 kg/d, respectively. The increase in milk yield induced by the growth hormone-releasing factor was greater than that for bST. Milk yield was not different among groups following cessation of treatment. Milk energy output was 24.2 Mcal/d in controls, and growth hormone-releasing factor increased milk energy output to 28.5 Mcal/d. Milk energy output of cows receiving bST was 26.1 Mcal/d. Growth hormone-releasing factor increased DMI (23.2 kg/d) over that of controls (21.1 kg/d), whereas bST (21.5 kg/d) did not. Relative to controls, bST increased averaged daily serum somatotropin from 1.3 to 7.6 ng/ml and insulin-like growth factor-I from 67.5 to 116.0 ng/ml. Relative to bST, growth hormone-releasing factor increased serum somatotropin to 16.3 ng/ml and insulin-like growth factor-I to 202.6 ng/ml. Relative to control (115.8 meq/dl) and bST (158.1 meq/dl), growth hormone-releasing factor increased plasma NEFA (230.3 meq/dl). During treatment, calculated energy balance was negative for cows receiving growth hormone-releasing factor but positive for bST and control cows. Milk composition, body condition score, BW, and apparent digestibility of DM were not different among treatments. We conclude that i.v. infusion of 12 mg/d mg of growth hormone-releasing factor has greater galactopoietic activity than i.m. injections of 14 mg/d of bST.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Temperature effects on serum prolactin concentrations and activity of dopaminergic neurons in the infundibulum/pituitary stalk of calves.

The effects of ambient temperature on serum concentrations of prolactin and neurochemical estimates of activity of dopaminergic neurons projecting to the infundibulum/pituitary stalk were investigated in Holstein bull calves. Accumulation of 3,4-dihydroxyphenylalanine (DOPA) in the infundibulum/pituitary stalk after intravenous injection of a decarboxylase inhibitor was used to estimate activity of these dopaminergic neurons. Increasing ambient temperature from 21 to 33 degrees C for 22 hr increased serum concentrations of prolactin and decreased activity of the dopaminergic neurons. Conversely, reducing ambient temperature from 22 degrees C to 11 degrees C decreased serum concentrations of prolactin and increased activity of these dopaminergic neurons. It is suggested that alterations in activity of dopaminergic neurons terminating in the infundibulum/pituitary stalk of bull calves may mediate acute temperature-induced changes in secretion of prolactin.

Acclimatization↗

PubMed1990

Sixty-day infusions of somatotropin-releasing factor stimulate milk production in dairy cows.

Twenty-four Holstein cows were infused intravenously with sterile water (placebo) or 1,3, or 12 mg of recombinant bovine somatotropin-releasing factor 1-45-homoserine lactone/d for 60 d. Relative to placebo (22.8 kg/d), 3 and 12 mg of somatotropin-releasing factor increased yield of milk to 28.8 and 33.3 kg/d during infusion. At 1 mg of somatotropin-releasing factor, milk averaged 27.5 kg/d during infusion but was increased above placebo only through 39 d. After infusion of 12 mg somatotropin-releasing factor ended, milk (26.4 kg/d) remained above placebo amounts (20.6 kg/d) for 15 d. Three and 12 mg of somatotropin-releasing factor increased serum somatotropin from .7 (placebo) to 8.2 and 10.3 ng/ml when averaged across 1, 30, and 59 d, whereas 1 mg increased somatotropin to 5.8 ng/ml after 1 d but had no effect at 30 or 59 d. Within 17 h of cessation of somatotropin-releasing factor infusion, serum concentrations of somatotropin were similar across all groups. On d 59, 3 and 12 mg infusions increased insulin-like growth factor I from 115.8 (placebo) to 204.7 and 261.4 ng/ml of serum. We conclude that somatotropin-releasing factor increased serum concentrations of somatotropin and milk yield in a dose-dependent manner for at least 60 d. Also galactopoietic effects of somatotropin-releasing factor persisted for 15 d independent of increased concentrations of somatotropin in serum following withdrawal of somatotropin-releasing factor.

Animals↗

PubMed1990

Prolactin regulation of dopaminergic neurons in the infundibulum pituitary stalk of bull calves.

The effects of elevated circulating concentrations of prolactin were examined on neurochemical estimates of activity of dopaminergic neurons in the infundibulum/pituitary stalk of Holstein bull calves (8-10 weeks of age). Activity of these neurons was estimated by measuring the accumulation of dihydroxyphenylalanine, the immediate precursor of dopamine, 15 min after an intravenous injection of the aromatic L-amino acid decarboxylase inhibitor, 3-hydroxybenzylhydrazine. Subcutaneous injections of the dopamine antagonist haloperidol every 6 hr for 1 day increased serum concentrations of prolactin and accumulation of dihydroxyphenylalanine in the infundibulum/stalk. Intravenous infusions of prolactin for 1 or 9 days increased accumulation of dihydroxyphenylalanine in the infundibulum/stalk, indicating that these neurons remain responsive to elevated prolactin for at least 9 days. It is concluded that elevated concentrations of prolactin in blood stimulate dopaminergic neurons in the infundibulum/pituitary stalk of bull calves. We speculate that these neurons may be analogous to the tuberoinfundibular dopaminergic neurons that regulate prolactin in rats.

Animals↗

PubMed1990

Influence of melatonin on mammary gland growth: in vivo and in vitro studies.

Our objective was to determine whether melatonin influenced mammary growth in response to mammogenic hormones. Prepubertal female BALB/c mice were injected for 9 days with 1 microgram of 17 beta-estradiol and 1 mg of progesterone or 17 beta-estradiol/progesterone plus 50, 100, or 200 micrograms of melatonin. Area of the parenchyma and total DNA content of the second thoracic gland were similar between controls and melatonin-injected mice. However, micrograms of DNA/100 mg of mammary tissue were lower in animals treated with 17 beta-estradiol/progesterone plus 200 micrograms of melatonin than in controls. Triglyceride content of mammary glands from animals treated with 100 or 200 micrograms of melatonin/day increased relative to controls. In an in vitro experiment, thoracic mammary glands of 21-day-old mice were cultured for 6 days in a mammogenic milieu of hormones (17 beta-estradiol/progesterone, aldosterone, bovine prolactin, growth hormone, and insulin) with 0 (control), 10(-6), 10(-9), or 10(-12) M melatonin. Relative to controls, 10(-12) M melatonin increased and 10(-6) M melatonin decreased mammary DNA and uptake of [methyl-3H]thymidine. We conclude that high doses of melatonin reduce mammary development in normal mice and that some of this effect may be mediated directly at the mammary tissue.

Animals↗

PubMed1989

Effects of infusions of various doses of bovine growth hormone-releasing factor on blood hormones and metabolites in lactating Holstein cows.

In two experiments, the effects of i.v. infusions of various doses of bovine GH-releasing factor (GRF) on blood hormones and metabolites in lactating Holstein cows were determined. In experiment 1, cows were infused with GRF (0, 3.125, 6.25, 12.5, 25.0 or 50.0 mg/cow per 24 h) for 24 h. Blood was sampled at -1, 5, 11, 15 and 23 h relative to the start of the infusion. The serum concentration of somatomedin C (SM-C) before infusion was 303 +/- 8 (S.E.M.) micrograms/l. Doses of GRF of between 3.125 and 50.0 mg were equipotent in stimulating (P less than 0.05) SM-C by 1.5- to 2.5-fold. GRF-induced increases in SM-C occurred by 11 h from the start of the infusion. In experiment 2, primiparous cows were infused with GRF (0, 1 or 3 mg/24 h) for 20 days. Blood was sampled for 12 h on days 1, 10 and 19. The 1 mg dose of GRF increased (P less than 0.05) blood concentrations of SM-C (on days 10 and 19) and glucose (on day 19), but did not affect blood concentrations of prolactin, insulin, cortisol, tri-iodothyronine (T3), thyroxine (T4), non-esterified fatty acids (NEFA) or glucose. The 3 mg dose of GRF increased (P less than 0.05) blood concentrations of SM-C (on days 10 and 19), T3 (on days 10 and 19), insulin (on day 19), NEFA (on days 1, 10 and 19) and glucose (on day 19), but did not affect blood concentrations of prolactin, cortisol or T4. We conclude that these data are consistent with the hypothesis that the galactopoietic effect of exogenous GRF in dairy cattle is mediated by increased secretion of GH.

Animals↗

PubMed1989

Failure of photoperiod to alter body growth and carcass composition in beef steers.

In each of two experiments, 70 crossbred steers were blocked by BW and assigned to initial slaughter groups or to treatments in a 2 x 2 design. In Exp. 1, treatments were 168 d of photoperiod (8 h of light [L]:16 h of dark [D] or 16L:8D) and plane of nutrition (high energy [HPN] or low energy [LPN]). On d -22, 67 and 155, blood was sampled every 20 min for 8 h. Relative to LPN, HPN increased (P less than .01) ADG by 28%, carcass weight by 26% and accretion of carcass fat by 109% and carcass protein by 20%. On d 155, compared with LPN, HPN increased (P less than .01) serum insulin (INS; 1.09 vs .64 ng/ml) and lowered (P less than .05) growth hormone (GH; 2.14 vs 3.70 ng/ml), but prolactin was not affected. Photoperiod did not affect BW gains, carcass composition or serum hormones. In Exp. 2, treatments were 113 d of photoperiod (8L:16D or 16L:8D) and Synovex-S implant (presence [IMP] or absence [NONIMP]). On d 93, blood was sampled every 30 min for 10 h. Relative to NONIMP, IMP increased (P less than .01) ADG by 12% and accretion of carcass protein by 16%. Implants did not affect carcass weight or accretion of fat. Compared with NONIMP, IMP increased (P less than .05) GH (3.16 vs 2.39 ng/ml) and INS (.68 vs .46 ng/ml) but did not affect PRL. Photoperiod did not affect BW gain, carcass composition or serum hormones. We conclude that photoperiod fails to influence growth and carcass composition of steers.

Analysis of Variance↗

PubMed1989

Daily changes in concentrations of prolactin in serum of prepubertal bulls exposed to short- or long-day photoperiods.

Early temporal changes in concentrations of prolactin (PRL) in serum after a sudden change in photoperiod and daily responsiveness to PRL-releasing and inhibiting factors were investigated in prepubertal Holstein bull calves exposed to different photoperiods. In calves switched from 8-hr light: 16-hr dark to 16-hr light:8-hr dark, there was no observable change in the daily pattern of serum concentrations of PRL after 1, 2, or 4 days. On the other hand, in animals switched from 16-hr light:8-hr dark to 8-hr light:16-hr dark, there was a consistent increase in serum PRL from 33.4 ng/ml on Day 0 to maximum values of 57.3, 62.7, and 78.9 ng/ml between 14 and 18 hr after onset of light on Days 1, 2, and 4, respectively. Thus, absence of light allowed expression of a daily rhythm in serum concentrations of PRL that persisted for at least 4 days after the photoperiod switch. There were no differences in L-dopa inhibition of PRL release in animals exposed to 16-hr light:8-hr dark at 3 or 15 hr after onset of light. However, thyrotropin-releasing hormone-induced release of PRL was greater 3 hr after onset of light (11 hr after onset of dark) compared with release at 9, 15, and 21 hr after onset of light in animals exposed to 16-hr light:8-hr dark, but not in bulls exposed to 8-hr light:16-hr dark. The results provide evidence that the cue for the putative photosensitive period of PRL secretion in cattle may be more closely associated with onset of dark, not onset of light.

Animals↗

PubMed1989

Alterations in concentrations of dihydroxyphenylacetic acid in the median eminence of rats euthanatized with pentobarbital.

Concentrations of dopamine (DA) and one of its major metabolites, dihydroxyphenylacetic acid (DOPAC), were determined in selected brain regions of rats that were euthanatized either by decapitation or by intravenous injections of pentobarbital or Fatal Plus, a commercial preparation that contains pentobarbital. When compared with values in decapitated brains, pentobarbital increased the concentration of DOPAC in the median eminence, which contains terminals of tuberoinfundibular dopaminergic (TIDA) neurons. Fifteen minutes of restraint reduced the concentration of DOPAC in the median eminence of rats killed by decapitation or by injections of pentobarbital, indicating that pentobarbital does not mask restraint-induced decrease in TIDA neuronal activity. In contrast, none of the manipulations altered DA or DOPAC concentrations in the striatum, which contains terminals of nigrostriatal dopaminergic neurons. Thus, changes in the concentrations of DOPAC in the median eminence (an index of TIDA neuronal activity) induced by stress can be detected in rats euthanatized by either decapitation or an injection of pentobarbital.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1988

Mammary lipoprotein lipase in plasma of cows after parturition or prolactin infusion.

Plasma lipase activity from the mammary vein and a tail blood vessel was measured in periparturient Holstein cows treated in one of three ways: control, CB154 (2-Br-alpha-ergocryptin) or CB154 plus prolactin. CB154 administration decreased basal serum prolactin concentration by 80% and blocked the normal parturient increase of serum prolactin. In CB154 plus prolactin-treated cows, prolactin was infused continuously for six days starting five and eight days prepartum. Plasma lipase activity was not detectable up to 26 hr prepartum in control and CB154-treated cows or before the start of prolactin infusion in CB154 plus prolactin-treated cows. After two hr prepartum, plasma lipase activity was detected in all treatments. In CB154 plus prolactin-treated cows, plasma lipase activity was detected in the presence of high concentrations of serum progesterone four days after the start of prolactin infusion and at least two days before parturition. Plasma lipase activity was four times greater in the mammary vein than in the tail vessel at sampling times at which activity was detected in both vessels. We propose the difference between plasma lipase activity from the mammary vein and tail vessel is due to release of lipoprotein lipase from the mammary gland into blood, and this activity can be induced prepartum by prolactin or at parturition even if the parturient increase in prolactin is suppressed.

Animals↗

PubMed1988

Growth, carcass composition and plasma melatonin in postpubertal beef heifers fed melatonin.

Two experiments were conducted to determine if feeding melatonin alters plasma concentrations of melatonin, growth and carcass composition of postpubertal beef heifers exposed to 16 h light (L):8 h dark (D). In Exp. 1, 16 heifers were blocked by initial body weight (318 +/- 5.6 kg). Four heifers were killed before starting the melatonin treatment to obtain initial carcass composition. Six heifers received vehicle (95% ethanol) and six were fed melatonin (4 mg/100 kg body weight) daily for 58 d at 1330 to coincide with the middle of the 16-h light period. On d 59 heifers were slaughtered. Melatonin feeding increased the percentage of fat in rib (P less than .05) and longissimus muscle (LD; P less than .10) and carcass fat accretion 28% (P less than .09) but reduced the percentage of protein 8% in rib (P less than .05) and carcass protein accretion 30% (P less than .09). Other measures in the carcass and body weight gain were not affected (P greater than .10) by feeding melatonin. Plasma concentrations of melatonin increased (P less than .01) from 10 to 140 pg/ml within 30 min of feeding melatonin. In Exp. 2, 24 heifers were blocked by initial body weight (348 +/- 13.7 kg). Eight heifers were killed initially, eight received vehicle and eight were fed melatonin for 63 d as described in Exp. 1. Melatonin did not influence (P greater than .10) body weight gain or any measure in the carcass; however, these heifers were fatter (40.1%) than those in Exp. 1 (30.9%) at the beginning of the experiment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Effect of pinealectomy on prolactin, testosterone and luteinizing hormone concentration in plasma of bull calves exposed to 8 or 16 hours of light per day.

Pineal tissue was removed from eight 6-wk-old bull calves (PX), whereas eight similar calves received sham pinealectomies (SPX). Before and after surgery, calves received 8 h of light (L):16 h of darkness (D) daily until 20 wk of age (wk 0 of experiment), at which time eight calves (four PX and four SPX) were maintained under 8L:16D for 12 additional wk, whereas the remaining eight calves received 16L:8D. At 0, 4, 8 and 12 wk of experiment, blood was collected from each animal for 26 h at 30-min intervals. Melatonin in SPX calves at wk 12 increased from 16.2 pg/ml of plasma when lights were on to 81.6 pg/ml during lights off, whereas in PX calves the nocturnal increase was absent. However, the nocturnal surge did occur in three PX calves on 8L:16D treatment, and those animals were excluded from calculations and analysis. At wk 0, prolactin (PRL) averaged 47 ng/ml among all calves. By wk 4 PRL increased (P less than .01) to 80 and 96 ng/ml in PX and SPX calves receiving 16L:8D, respectively; PRL averaged 53 and 48 ng/ml, respectively in PX and SPX calves maintained on 8L:16D. Prolactin was greater (P less than .05) through wk 12 in PX (64 ng/ml) and SPX (64 ng/ml) calves receiving 16L:8D than in calves exposed to 8L:16D, which remained unchanged (54 and 48 ng/ml). Testosterone was unaffected by photoperiod, but tended to be less (P = .13) in plasma of PX than of SPX calves at wk 0 (.90 vs 1.45 ng/ml of plasma).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗