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Diurnal variations in serum luteinizing hormone, growth hormone, and prolactin concentrations in intact and pinealectomised chickens
GENERAL
AND
COMPARATtVE
ENDOCRINOLOGY
41, 266-269 (1980)
NOTES Diurnal
Variations in Serum Luteinizing Hormone, Growth and Prolactin Concentrations in Intact and Pinealectomised Chickens
Hormone,
Diurnal variations in luteinizing hormone and prolactin have been demonstrated in sera from immature cockerels. Pinealectomy significantly altered these patterns of hormone secretion. No diurnal pattern in growth hormone concentration was seen in intact or pinealectomised birds. -
INTRODUCTION
In mammals, diurnal rhythms in luteinizing hormone (LH) (Dunn et al., 1972), growth hormone (GH) (Quabbe et al., 1966), and prolactin (Sassin et al., 1972) secretion have clearly been demonstrated. In contrast, although a diurnal rhythm in LH secretion has been seen in some avian studies (Wilson and Sharp, 1973; Bolton et al., 1974; Scanes et al., 1978), other investigations in birds (Nicholls et al., 1973; Gledhill and Follett, 1976; Balthazart et al., 1977) have not revealed such patterns and diurnal rhythms in GH and prolactin secretion have not been established in avian species. Therefore, in the present study we have determined daily variations in serum levels of LH, GH, and prolactin in immature male chickens. In addition, in view of the circadian rhythm of pineal activity in the domestic fowl (Pang et al., 1974; Binkley et al., 1975) and the fact that gonadotrophin (Orts and Benson, 1973; Orts et al., 1974), prolactin (Relkin et al., 1972; Reiter, 1975), and GH (Relkin, 1972) secretion may be affected by the pineal, the pattern of daily changes in circulating hormone levels were also determined in pinealectomised birds. MATERIALS
AND METHODS
Male White Leghorn chicks were reared at 24°C on floor pens on a long daily photoperiod (16L:8D) with access to a commercial diet and water. At 1 day of age the chicks were randomly distributed into two groups and the birds of one group were pinealectomised (Foss 266 0016~6480/80/060266-04$01.00/O Copyright All rights
@ 1980 by Academic Press. Inc. of reproduction in any form reserved.
et al., 1972). Terminal blood samples were taken at 3-hr intervals by cardiac puncture from groups of eight control and eight pinealectomised birds when 8 weeks old. During the scotophase, the birds were bled in the absence of any supplementary lighting. After separation, sera were stored at -20°C prior to analysis. The completeness of pinealectomy was checked at autopsy by gross visual examination and samples from birds where surgery had not been complete were excluded from analysis. Sera concentrations of the pituitary hormones were determined using specific homologous radioimmunoassays for LH (Follett et al., 1972), GH (Harvey and Scanes, 1977), and prolactin (Scanes et al., 1976). Each serum was assayed in duplicate and all of the samples were assayed in single assays to eliminate interassay variation. The results were examined for statistical differences by Student’s t test and for cyclical patterns by the method of Halberg et al. (1972).
RESULTS
Daily variations in the concentrations of the circulating hormones are shown in Fig. 1. There was a striking (p < 0.01) increase (154% over the preceding value) in serum LH levels at the onset of the dark period. The LH concentration fell progressively thereafter during the dark but remained significantly (p < 0.05) higher than the level at the beginning and end of the light period. The mean LH level during the dark (7.80 f (SEM) 0.90 (n = 24) rig/ml) was significantly higher (p < 0.001) than that in the light (4.07 + 0.26 (n = 48) q/ml). This variation in LH concentration was clearly cyclical (p = 4.64 x 10e6) and could be fitted to a sinusoidal curve with an acrophase 2.9 hr after the onset of the dark period. No
NOTES
267
tomised birds (Fig. l), although the mean GH level in the pinealectomised birds during the dark (26 + 2 (n = 24) @ml) was lower (p < 0.05) than the corresponding level in the controls (32 ? 2 (n = 24) &ml) and lower (p < 0.05) than the mean GH concentration in the pinealectomised birds during the light period (35 f 2 (n = 48) t&ml).
loLH Ing/mll 5
lOOGH IngAnll
DISCUSSION
70-1 I 0900
' I
1 1500
I I I 2100 Time Ihoursl
I 0300
0900
FIG. 1. Daily variations in the concentrations of LH, GH, and prolactin in intact (---I and pinealectomised C----J chickens.
such pattern in serum LH levels was seen during the sampling period in pinealectomised birds. In the intact birds the prolactin concentration increased toward the end of the dark period in a sinusoidal pattern (p = 0.023) and remained elevated at the beginning of the photophase (Fig. 1). This peak (between 0300 and 0900 hr) was significantly (p < 0.05) higher than the level in the preceding 12-hr period. Maximum prolactin levels were also found at this time in the pinealectomised birds although the levels were also high at 1800 hr and this pattern could not be fitted to a sinusoidal curve (p = 0.056). Mean circulating prolactin concentrations during the day (intact, 126 2 4 (n = 48) rig/ml; pinealectomised 105 & 5 (n = 48) rig/ml) tended to be lower (p < 0.05) in the pinealectomised birds and were significantly lower (p < 0.05) at 0900 and 1200 hr. There was no evidence of a daily rhythm of GH secretion in intact or pinealec-
The finding of nocturnal increases in circulating LH levels in the present study confirms previous findings in domestic fowl (Scanes et al., 1978) and these nocturnal peaks also coincide with those reported for pineal, hypothalamic, and circulating melatonin concentrations (Pang et al., 1974; Binkley et al., 1975). The absence of the nocturnal increase in LH levels following pineal ablation might therefore suggest the involvement of the pineal body in the control of its release. This finding is further supported by the fact that ovarian development and the onset of lay in Japanese quail are delayed, albeit transiently, in pinealectomised birds, presumably because of inhibition of gonadotropin secretion (Saylor and Wolfson, 1967). Ralph (1970) has also observed an inhibitory effect of pinealectomy on gonadal activity in Japanese quail. Whether this nocturnal increase in circulating LH level results from an increase in pituitary LH secretion rate or reflects a change in its half-life is not known and awaits further investigation. In the present study the nocturnal increase in circulating prolactin levels in both intact and pinealectomised birds is similar to that reported in man (Sassin et al., 1972), cattle (Koprowski et al., 1972), rats (Dunn et al., 1972), and mice (Sinha et al., 1977). Kizer ef al. (1975) have also found that pinealectomy does not abolish the nyctohemeral rhythm of plasma prolactin in male rats. The low prolactin level in the pinealectomised birds during the first 6 hr of the light period is similar to the depres-
NOTES
268
sive effect of pinealectomy on plasma prolactin concentrations in rats during the early photophase of a diurnal lighting regimen (Relkin et al., 1972). The lack of a distinct daily pattern of GH release in the immature cockerel (Fig. 1) agrees with a previous finding in mature hens (Harvey ef al., 1979) but is in marked contrast with mammalian studies (e.g., Quabbe ef al., 1966) in which diurnal patterns of GH secretion characteristically occur. The reason for this difference is uncertain but may reflect differences in feeding or sleeping patterns. The failure of pinealectomy to alter GH levels in the chicken also suggests that the control of GH secretion in the bird differs from that in mammals, in which pinealectomy (Relkin, 1972) or the administration of pineal indoles (Smythe er al., 1976) affects blood GH levels. ACKNOWLEDGMENT This work was partly supported by a grant from the Science Research Council (GR/A 29869) to Professor J. G. Phillips.
REFERENCES Balthazart, J., Hendrick, J. C., and Deviche, P. (1977). Diurnal variations of plasma gonadotrophins in male domestic ducks during the sexual cycle.
Gen.
Comp.
Endocrinol.
32, 376-389.
Binkley, S., MacBridge, S. E., Klein, D. C., and Ralph, C. L. (1975). Regulation of pineal rhythms in chickens: Refractory period and non visual light perception. Endocrinology 96, 848-853. Bolton, N. J., Chadwick, A., Chapman, H. M., Hall, T. R., and Scanes, C. G. (1974). Diurnal fluctuations in hormone levels in pituitary and plasma LH in the juvenile domestic cockerel. J. Endocrinol. 63, 63P. Dunn, J. S., Arimura, A., and Scheving, L. E. (1972). Effect of stress on circadian periodicity in serum LH and prolactin concentration. Endocrinology 90, 23-33. Follett, B. K., Scanes, C. G., and Cunningham, F. J. (1972). A radioimmunoassay for avian luteinizing hormone. J. Endocrinol. 52, 359-378. Foss, D. C., Machemer, R. H., and Carew, L. B., Jr. (1972). Surgical removal of the pineal gland in 3-5 day old chicks. Proc. Sot. Exp. Biol. Med. 139, 1451-1453. Gledhill, B., and Follett, B. K. (1976). Diurnal varia-
tion and the episodic release of plasma gonadotrophins in Japanese quail during a photoperiodically-induced gonadal cycle. J. Endocrinol. 71, 245-257. Halberg, F., Johnson, E. A., Nelson, W., Reinge, W., and Sothern, R. (1972). Autorhythmetry procedures for physiologic self-measurements and their analysis. Physiol. Teacher 1, l- 11. Harvey, S., and Scanes, C. G. (1977). Purification and radioimmunoassay of chicken growth hormone. J. Endocrinol.
73, 321-329.
Harvey, S., Scanes, C. G., and Sharp, P. J. (1979). Variations in plasma growth hormone concentrations in laying hens. Brit. Poulr. Sci. 20, 163- 166. Kizer, J. S., Ziuin, J. A., Jacobowitz, D. M., and Kopin, I. J. (1975). The nyctohemeral rhythm of plasma prolactin: Effects of ganglionectomy, pinealectomy, constant light, constant darkness or 6-OH-dopamine administration. Endocrinology 96, 1230- 1240. Koprowski, J. A., Tucker, H. A.. and Convey, E. M. (1972). Prolactin and growth hormone circadian periodicity in lactating cows. Proc. Sot. Exp. Biol. Med. 140, 1012-1014. Nicholls, T. J., Scanes, C. G., and Follett, B. K. (1973). Plasma and pituitary luteinizing hormone in Japanese quail during photoperiodically induced gonadal growth and regression. Gen. Comp. Endocrinol. 21, 84-98. Orts, R. J., and Benson, B. (1973). Inhibitory effects on serum and pituitary LH by a melatonin-free extract of bovine pineal glands. Life Sci. 12, 513-519. Orts,R. J.,Benson,B.,andCook,B. F.(1974). Some antigonadotrophic effects of melatonin-free bovine pineal extracts in rats. Acfa Endocrinol. 76, 438-448. Pang, S. F., Ralph, C. L., and Reilly, D. P. (1974). Melatonin in the chicken brain: Its origin, diurnal variation and regional distribution. Gen. Comp. Endocrinol.
22, 499-506.
Quabbe, H. J., Schilling, E., and Helge, H. (1966). Pattern of growth hormone secretion during a 24hour fast in normal adults. J. C/in. Endocrinol. Mefab. 26, 1 l73- 1177. Ralph, C. L. (1970). The structure and alleged function of avian pineals. Amer. Zoo/. 10, 217-235. Reiter, R. J. (1975). Changes in pituitary prolactin levels of female hamsters as a function of age, photoperiod and pinealectomy. Acfa Endocrinol. 79,43-50. Relkin, R. (1972). Effects of pinealectomy, constant light and darkness on growth hormone levels in the pituitary and plasma of the rat. J. Endocrinol. 53, 289-293. Relkin, R., Adachi, M., and Kahan, S. A. (1972). Effects of pinealectomy and constant light and darkness on prolactin levels in the pituitary and plasma
NOTES and on pituitary ultrastructure docrinol.
54,
of the rat. ./.
En-
263-268.
Sassin, J. F., Frantz, A. G., Weiztmann, E. D., and Kapen, S. (1972). Hormone prolactin: 24-hour pattern with increased release during sleep. Science 177, 12055 1207. Saylor, A., and Wolfson, A. (1967). The avian pineal gland. Science 158, 1478- 1479. Scanes, C. G., Chadwick, A., and Bolton, N. J. (1976). Radioimmunoassay of prolactin in the plasma of the domestic fowl. Gen. Comp. Endocrinol. 30, 12-20. Scanes, C. G., Chadwick, A., Sharp, P. J., and Bolton, N. J. (1978). Diurnal variation of plasma luteinizing hormone levels in the domestic fowl (Callus
domesticus).
Gen.
Comp.
Endocrinol.
plasma LH levels during the ovulatory cycle of the hen, Gallus domesticus. J. Reprod. Fe&i. 35, 561-564. C. G. SCANES Department of Physiology Rutgers Uniraersity New Brunswick, New Jersey
08903
S. HARVEY Woljson
Institute
University Hull HU6
of Hull 7RX, England
34,
45-49. Sinha, Y. N., Salcocks, C. B., Wickes, M. A., and Vanderlaan, W. P. (1977). Serum and pituitary concentration of prolactin and growth hormone in mice during a twenty-four hour period. Endocrinology
269
A. CHADWICK Department University Leeds LS2
of Pure
and
Applied
Zoology
of Leeds 9JT. England
100,786-791.
Smythe, A., Compton, P. J., and Lazarus, L. (1976). Serotoninergic control of human growth hormone secretion: The actions of 1-dopa and 2-bromo-oergocryptine. In “Frontiers in Neuroendocrinology,” Vol. 4 (L. Martin and W. F. Garong, eds.), pp. 222-23.5. Raven, New York. Wilson, S. C., and Sharp, P. J. (1973). Variations in
L. GALES W. S. NEWCOMER Department Oklahoma
of Physiological State University
Stillwater, Accepted
Oklahoma December
Sciences
74074 I3* 1979
AND
COMPARATtVE
ENDOCRINOLOGY
41, 266-269 (1980)
NOTES Diurnal
Variations in Serum Luteinizing Hormone, Growth and Prolactin Concentrations in Intact and Pinealectomised Chickens
Hormone,
Diurnal variations in luteinizing hormone and prolactin have been demonstrated in sera from immature cockerels. Pinealectomy significantly altered these patterns of hormone secretion. No diurnal pattern in growth hormone concentration was seen in intact or pinealectomised birds. -
INTRODUCTION
In mammals, diurnal rhythms in luteinizing hormone (LH) (Dunn et al., 1972), growth hormone (GH) (Quabbe et al., 1966), and prolactin (Sassin et al., 1972) secretion have clearly been demonstrated. In contrast, although a diurnal rhythm in LH secretion has been seen in some avian studies (Wilson and Sharp, 1973; Bolton et al., 1974; Scanes et al., 1978), other investigations in birds (Nicholls et al., 1973; Gledhill and Follett, 1976; Balthazart et al., 1977) have not revealed such patterns and diurnal rhythms in GH and prolactin secretion have not been established in avian species. Therefore, in the present study we have determined daily variations in serum levels of LH, GH, and prolactin in immature male chickens. In addition, in view of the circadian rhythm of pineal activity in the domestic fowl (Pang et al., 1974; Binkley et al., 1975) and the fact that gonadotrophin (Orts and Benson, 1973; Orts et al., 1974), prolactin (Relkin et al., 1972; Reiter, 1975), and GH (Relkin, 1972) secretion may be affected by the pineal, the pattern of daily changes in circulating hormone levels were also determined in pinealectomised birds. MATERIALS
AND METHODS
Male White Leghorn chicks were reared at 24°C on floor pens on a long daily photoperiod (16L:8D) with access to a commercial diet and water. At 1 day of age the chicks were randomly distributed into two groups and the birds of one group were pinealectomised (Foss 266 0016~6480/80/060266-04$01.00/O Copyright All rights
@ 1980 by Academic Press. Inc. of reproduction in any form reserved.
et al., 1972). Terminal blood samples were taken at 3-hr intervals by cardiac puncture from groups of eight control and eight pinealectomised birds when 8 weeks old. During the scotophase, the birds were bled in the absence of any supplementary lighting. After separation, sera were stored at -20°C prior to analysis. The completeness of pinealectomy was checked at autopsy by gross visual examination and samples from birds where surgery had not been complete were excluded from analysis. Sera concentrations of the pituitary hormones were determined using specific homologous radioimmunoassays for LH (Follett et al., 1972), GH (Harvey and Scanes, 1977), and prolactin (Scanes et al., 1976). Each serum was assayed in duplicate and all of the samples were assayed in single assays to eliminate interassay variation. The results were examined for statistical differences by Student’s t test and for cyclical patterns by the method of Halberg et al. (1972).
RESULTS
Daily variations in the concentrations of the circulating hormones are shown in Fig. 1. There was a striking (p < 0.01) increase (154% over the preceding value) in serum LH levels at the onset of the dark period. The LH concentration fell progressively thereafter during the dark but remained significantly (p < 0.05) higher than the level at the beginning and end of the light period. The mean LH level during the dark (7.80 f (SEM) 0.90 (n = 24) rig/ml) was significantly higher (p < 0.001) than that in the light (4.07 + 0.26 (n = 48) q/ml). This variation in LH concentration was clearly cyclical (p = 4.64 x 10e6) and could be fitted to a sinusoidal curve with an acrophase 2.9 hr after the onset of the dark period. No
NOTES
267
tomised birds (Fig. l), although the mean GH level in the pinealectomised birds during the dark (26 + 2 (n = 24) @ml) was lower (p < 0.05) than the corresponding level in the controls (32 ? 2 (n = 24) &ml) and lower (p < 0.05) than the mean GH concentration in the pinealectomised birds during the light period (35 f 2 (n = 48) t&ml).
loLH Ing/mll 5
lOOGH IngAnll
DISCUSSION
70-1 I 0900
' I
1 1500
I I I 2100 Time Ihoursl
I 0300
0900
FIG. 1. Daily variations in the concentrations of LH, GH, and prolactin in intact (---I and pinealectomised C----J chickens.
such pattern in serum LH levels was seen during the sampling period in pinealectomised birds. In the intact birds the prolactin concentration increased toward the end of the dark period in a sinusoidal pattern (p = 0.023) and remained elevated at the beginning of the photophase (Fig. 1). This peak (between 0300 and 0900 hr) was significantly (p < 0.05) higher than the level in the preceding 12-hr period. Maximum prolactin levels were also found at this time in the pinealectomised birds although the levels were also high at 1800 hr and this pattern could not be fitted to a sinusoidal curve (p = 0.056). Mean circulating prolactin concentrations during the day (intact, 126 2 4 (n = 48) rig/ml; pinealectomised 105 & 5 (n = 48) rig/ml) tended to be lower (p < 0.05) in the pinealectomised birds and were significantly lower (p < 0.05) at 0900 and 1200 hr. There was no evidence of a daily rhythm of GH secretion in intact or pinealec-
The finding of nocturnal increases in circulating LH levels in the present study confirms previous findings in domestic fowl (Scanes et al., 1978) and these nocturnal peaks also coincide with those reported for pineal, hypothalamic, and circulating melatonin concentrations (Pang et al., 1974; Binkley et al., 1975). The absence of the nocturnal increase in LH levels following pineal ablation might therefore suggest the involvement of the pineal body in the control of its release. This finding is further supported by the fact that ovarian development and the onset of lay in Japanese quail are delayed, albeit transiently, in pinealectomised birds, presumably because of inhibition of gonadotropin secretion (Saylor and Wolfson, 1967). Ralph (1970) has also observed an inhibitory effect of pinealectomy on gonadal activity in Japanese quail. Whether this nocturnal increase in circulating LH level results from an increase in pituitary LH secretion rate or reflects a change in its half-life is not known and awaits further investigation. In the present study the nocturnal increase in circulating prolactin levels in both intact and pinealectomised birds is similar to that reported in man (Sassin et al., 1972), cattle (Koprowski et al., 1972), rats (Dunn et al., 1972), and mice (Sinha et al., 1977). Kizer ef al. (1975) have also found that pinealectomy does not abolish the nyctohemeral rhythm of plasma prolactin in male rats. The low prolactin level in the pinealectomised birds during the first 6 hr of the light period is similar to the depres-
NOTES
268
sive effect of pinealectomy on plasma prolactin concentrations in rats during the early photophase of a diurnal lighting regimen (Relkin et al., 1972). The lack of a distinct daily pattern of GH release in the immature cockerel (Fig. 1) agrees with a previous finding in mature hens (Harvey ef al., 1979) but is in marked contrast with mammalian studies (e.g., Quabbe ef al., 1966) in which diurnal patterns of GH secretion characteristically occur. The reason for this difference is uncertain but may reflect differences in feeding or sleeping patterns. The failure of pinealectomy to alter GH levels in the chicken also suggests that the control of GH secretion in the bird differs from that in mammals, in which pinealectomy (Relkin, 1972) or the administration of pineal indoles (Smythe er al., 1976) affects blood GH levels. ACKNOWLEDGMENT This work was partly supported by a grant from the Science Research Council (GR/A 29869) to Professor J. G. Phillips.
REFERENCES Balthazart, J., Hendrick, J. C., and Deviche, P. (1977). Diurnal variations of plasma gonadotrophins in male domestic ducks during the sexual cycle.
Gen.
Comp.
Endocrinol.
32, 376-389.
Binkley, S., MacBridge, S. E., Klein, D. C., and Ralph, C. L. (1975). Regulation of pineal rhythms in chickens: Refractory period and non visual light perception. Endocrinology 96, 848-853. Bolton, N. J., Chadwick, A., Chapman, H. M., Hall, T. R., and Scanes, C. G. (1974). Diurnal fluctuations in hormone levels in pituitary and plasma LH in the juvenile domestic cockerel. J. Endocrinol. 63, 63P. Dunn, J. S., Arimura, A., and Scheving, L. E. (1972). Effect of stress on circadian periodicity in serum LH and prolactin concentration. Endocrinology 90, 23-33. Follett, B. K., Scanes, C. G., and Cunningham, F. J. (1972). A radioimmunoassay for avian luteinizing hormone. J. Endocrinol. 52, 359-378. Foss, D. C., Machemer, R. H., and Carew, L. B., Jr. (1972). Surgical removal of the pineal gland in 3-5 day old chicks. Proc. Sot. Exp. Biol. Med. 139, 1451-1453. Gledhill, B., and Follett, B. K. (1976). Diurnal varia-
tion and the episodic release of plasma gonadotrophins in Japanese quail during a photoperiodically-induced gonadal cycle. J. Endocrinol. 71, 245-257. Halberg, F., Johnson, E. A., Nelson, W., Reinge, W., and Sothern, R. (1972). Autorhythmetry procedures for physiologic self-measurements and their analysis. Physiol. Teacher 1, l- 11. Harvey, S., and Scanes, C. G. (1977). Purification and radioimmunoassay of chicken growth hormone. J. Endocrinol.
73, 321-329.
Harvey, S., Scanes, C. G., and Sharp, P. J. (1979). Variations in plasma growth hormone concentrations in laying hens. Brit. Poulr. Sci. 20, 163- 166. Kizer, J. S., Ziuin, J. A., Jacobowitz, D. M., and Kopin, I. J. (1975). The nyctohemeral rhythm of plasma prolactin: Effects of ganglionectomy, pinealectomy, constant light, constant darkness or 6-OH-dopamine administration. Endocrinology 96, 1230- 1240. Koprowski, J. A., Tucker, H. A.. and Convey, E. M. (1972). Prolactin and growth hormone circadian periodicity in lactating cows. Proc. Sot. Exp. Biol. Med. 140, 1012-1014. Nicholls, T. J., Scanes, C. G., and Follett, B. K. (1973). Plasma and pituitary luteinizing hormone in Japanese quail during photoperiodically induced gonadal growth and regression. Gen. Comp. Endocrinol. 21, 84-98. Orts, R. J., and Benson, B. (1973). Inhibitory effects on serum and pituitary LH by a melatonin-free extract of bovine pineal glands. Life Sci. 12, 513-519. Orts,R. J.,Benson,B.,andCook,B. F.(1974). Some antigonadotrophic effects of melatonin-free bovine pineal extracts in rats. Acfa Endocrinol. 76, 438-448. Pang, S. F., Ralph, C. L., and Reilly, D. P. (1974). Melatonin in the chicken brain: Its origin, diurnal variation and regional distribution. Gen. Comp. Endocrinol.
22, 499-506.
Quabbe, H. J., Schilling, E., and Helge, H. (1966). Pattern of growth hormone secretion during a 24hour fast in normal adults. J. C/in. Endocrinol. Mefab. 26, 1 l73- 1177. Ralph, C. L. (1970). The structure and alleged function of avian pineals. Amer. Zoo/. 10, 217-235. Reiter, R. J. (1975). Changes in pituitary prolactin levels of female hamsters as a function of age, photoperiod and pinealectomy. Acfa Endocrinol. 79,43-50. Relkin, R. (1972). Effects of pinealectomy, constant light and darkness on growth hormone levels in the pituitary and plasma of the rat. J. Endocrinol. 53, 289-293. Relkin, R., Adachi, M., and Kahan, S. A. (1972). Effects of pinealectomy and constant light and darkness on prolactin levels in the pituitary and plasma
NOTES and on pituitary ultrastructure docrinol.
54,
of the rat. ./.
En-
263-268.
Sassin, J. F., Frantz, A. G., Weiztmann, E. D., and Kapen, S. (1972). Hormone prolactin: 24-hour pattern with increased release during sleep. Science 177, 12055 1207. Saylor, A., and Wolfson, A. (1967). The avian pineal gland. Science 158, 1478- 1479. Scanes, C. G., Chadwick, A., and Bolton, N. J. (1976). Radioimmunoassay of prolactin in the plasma of the domestic fowl. Gen. Comp. Endocrinol. 30, 12-20. Scanes, C. G., Chadwick, A., Sharp, P. J., and Bolton, N. J. (1978). Diurnal variation of plasma luteinizing hormone levels in the domestic fowl (Callus
domesticus).
Gen.
Comp.
Endocrinol.
plasma LH levels during the ovulatory cycle of the hen, Gallus domesticus. J. Reprod. Fe&i. 35, 561-564. C. G. SCANES Department of Physiology Rutgers Uniraersity New Brunswick, New Jersey
08903
S. HARVEY Woljson
Institute
University Hull HU6
of Hull 7RX, England
34,
45-49. Sinha, Y. N., Salcocks, C. B., Wickes, M. A., and Vanderlaan, W. P. (1977). Serum and pituitary concentration of prolactin and growth hormone in mice during a twenty-four hour period. Endocrinology
269
A. CHADWICK Department University Leeds LS2
of Pure
and
Applied
Zoology
of Leeds 9JT. England
100,786-791.
Smythe, A., Compton, P. J., and Lazarus, L. (1976). Serotoninergic control of human growth hormone secretion: The actions of 1-dopa and 2-bromo-oergocryptine. In “Frontiers in Neuroendocrinology,” Vol. 4 (L. Martin and W. F. Garong, eds.), pp. 222-23.5. Raven, New York. Wilson, S. C., and Sharp, P. J. (1973). Variations in
L. GALES W. S. NEWCOMER Department Oklahoma
of Physiological State University
Stillwater, Accepted
Oklahoma December
Sciences
74074 I3* 1979