Changes in serum concentration of luteinizing hormone in the female rat approaching puberty

Abstract

Concentrations of LH in the serum were estimated in rats bled either once or twice during a 15-day period preceding first ovulation. In rats bled once (between 09.00 and 17.00 h) serum concentrations showed little change between 15 and 9 days before first ovulation and averaged 16 micrograms/l (days -15 to -9). A shift in LH level, to a mean of 31 micrograms/l, was seen on day -8, whereafter LH concentrations increased gradually. Basal LH values of less than 10 micrograms/l were only found until day -4. The finding that LH values increased with age was confirmed by data from rats bled twice with an interval of greater than or equal to 3 days between bleedings. Furthermore, both in rats bled twice at 11.00 h and in rats bled twice at 15.00 h LH concentrations were significantly higher in the second sample. Both morning (11.00 h) and afternoon (15.00 h) LH concentrations in rats bled once also indicated a rise in LH concentrations with age but it became apparent that only morning values showed a shift in LH concentration (from approximately 15 to approximately 42 micrograms/l) from day -9 to day -8. In contrast, mean afternoon values showed a gradual increase from day -15 on. From day -8 on the number of rats with LH values greater than or equal to 50 micrograms/l increased, and from day -5 on they were more frequent at 15.00 than at 11.00 h. Thus a clear increase in LH secretion, most likely of a pulsatile nature, was found in the female rat approaching puberty. The correlation in time and possible functional relationship with late-prepubertal follicular growth is discussed.

Patterns of plasma LH, FSH, oestradiol and corticosteroids from birth to the first oestrous cycle in Meishan gilts

“…A similar period of high LH secretion around birth has been observed in calves (Challis et al, 1974), guinea-pigs (Donovan et al, 1975), humans (Kaplan and Grumbach, 1976) and rabbits (Berger et al, 1982 (Diekman et al, 1983) or at about 240 days (Camous el al, 1985). In agreement with our previous results in Large White gilts (Camous el al, 1985), (Boyar et al, 1974;Parker et al, 1975), in rats (Meijs-Roelofs et al, 1983;Urbanski and Ojeda, 1985) and in sheep (Foster et al, 1975;Foster and Ryan, 1981 (Rayford et al, 1974;Diekman et al, 1983;Camous et al, 1985) and in other species, such as sheep (Foster et al, 1975), rats (Dehler and Wuttke, 1975) and cattle (Schams et al, 1981). No significant variations in the concentration of plasma FSH were observed during the last weeks preceding puberty in agreement with Diekman et al (1983).…”

Association of Diurnal Variations in Hypothalamic but Not Cortical Opiate ([³H]-Naloxone)-Binding Sites with the Ability of Naloxone to Induce LH Release in the Prepubertal Female Rat

“…We were unable to detect a diurnal difference in basal LH levels, a result which appears to con flict with the results of Meijs-Roelofs et al (12]. Note, how ever, that our groups were very small compared with the hundreds of rats used by Meijs-Roelofs et al [12], We have, however, repeated and extended the observations of Blank and Mann [3] and have determined that this diurnal varia tion first appears between 23 and 26 days after birth, i.e., approximately 10 days before first ovulation in our colony. We have also shown that the minimal response to NAL is reflected in a similar change in the mediobasal hypotha lamic complement of opiate receptors.…”

“…This evidence, that as puberty approaches there may be a diurnal variation in the tonic opiate inhibition of gona dotrophin release, is supported by the findings of other in vestigators. Meijs-Roelofs et al [12] have found that from 5Received: April 14, 1986 Accepted after revision: July 30, 1986 days before the first ovulation, afternoon LH values were higher than in the morning. Urbanski and Ojeda [18] have also reported the development of a prepubertal increase in the amplitude of LH pulses in the afternoon, as well as the existence of an LH 'minisurge'.…”

Insulin-Like Growth Factor I: A Possible Metabolic Signal Involved in the Regulation of Female Puberty

“…During the juvenileperipubertal transition period, the pulsatile pattern of lutein izing hormone (LH) changes to a greater afternoon amplitude compared to the morning [1,2], This alteration in LH pulse amplitude indicates a change at the hypothalamic level since this has been shown to be a gonadal independent event [3]. Whether or not this activation of the LH-releasing hormone (LHRH) releasing system to a low morning-high afternoon pulsatile secretory mode is the result of the removal of an inhibi tory tone or the development of excitatory inputs governing LHRH release has yet to be clearly defined [2,3). However, recent studies in rodents and primates have implicated exci tatory amino acids acting via N-methyl-Z>-aspartate receptors as being physiologically involved in the initiation of puberty [4,5].…”