ACTIVITY OF THE PITUITARY-ADRENOCORTICAL SYSTEM AND THYROID GLAND DURING THE OESTROUS CYCLE OF THE RAT JULIA C.

BUCKINGHAM, K.-D. D\l=O"\HLER AND CATHERINE A. WILSON

Department of Pharmacology, Royal Free Hospital School of Medicine, 8 Hunter Street, London, WC1 1BP, *Endocrinology Clinic, The Medical School, Hannover, Germany and ^Department of Physiology, Royal Veterinary College, Royal College Street, London, NW1 OTU

(Received

December

1977)

SUMMARY

The concentrations of LH, progesterone, ACTH, corticosterone and thyroxine in the plasma estimated at various times during the oestrous cycle of the rat. The well-established patterns of LH and progesterone secretion were confirmed. On each day of the cycle the plasma concentrations of ACTH and corticosterone were lowest in the morning and rose in the afternoon. Conversely, during oestrus and dioestrus, the plasma concentrations of thyroxine were higher in the morning than in the evening. However, during the afternoon of pro-oestrus the concentrations of ACTH, corticosterone and thyroxine in the plasma rose and, like the concentrations of LH and progesterone, all reached levels far higher than those attained at any other time of the cycle. were

INTRODUCTION

The patterns of changes in the concentrations of gonadotrophins and gonadal steroids in the peripheral blood during the oestrous cycle of the rat are firmly established (Brown-Grant, Exley & Naftolin, 1970; Barraclough, Collu, Massa & Martini, 1971; Daane & Parlow, 1971 ; Butcher, Collins & Fugo, 1974). It appears that both the secretion of gonadotrophins and ovulation are influenced by changes in the functional activity of the adrenal cortices and thyroid gland (Bruni, Marshall, Dibbei & Meites, 1975; Mann, Korowitz & Barraclough, 1975; Peppier, Hess & Dunn, 1975; Dunn, Peppier, Hess & Johnson, 1976; Peppier & Jacobs, 1976). However, although some reports indicate that the hypersécrétion of luteinizing hormone (LH), follicle-stimulating hormone, prolactin and progesterone which normally occurs during pro-oestrus is accompanied by increases in pituitary-adrenocortical and pituitary-thyroid activity (Brown-Grant, 1962; Critchlow, Liebelt, Bar-Sela, Mount¬ castle & Lipscomb, 1963; Raps, Barthe & Desaulles, 1971; Brown, Courtney & Marotta, 1976; Brown-Grant, Dutton & ter Haar, 1977) few, if any, detailed studies concerning this aspect of endocrine physiology have been made. Accordingly we have estimated the plasma concentrations of corticotrophin (ACTH), corticosterone and thyroxine at various times during the oestrous cycle of the rat and have attempted to correlate them with the plasma concentrations of LH and progesterone. MATERIALS AND METHODS

Female

Sprague-Dawley temperature-controlled room

Animals (Tuck & Son) weighing 200-250 g were housed in a with a fixed lighting schedule (lights on 05.00-17.00 h). Food

rats

and water were available ad libitum. Vaginal smears were taken daily and thus the animals were accustomed to handling (Hodges & Mitchley, 1970). Only those rats which had at least three regular 4 day oestrous cycles were used for the experiments. id)

90

70

50

30

-

02.00 *

10.00

18.00

02.00

Pro-oestrus-^-

10

10 00 18.00 02.00 10.00 18.00 02.00 10.00 18.00 Oestrus -^-Dioestrus I->*-Dioestrus 2-> Time of

day (h)

Fig. 1. Concentrations of (a) LH (·) and progesterone (O), (¿>) corticotrophin (ACTH), (e) corti¬ costerone and (d) thyroxine in plasma at various times during the oestrous cycle of the rat. Each point is the mean of four (or eight,*) determinations and is shown with its standard error (standard errors omitted were always within ± 10% of the mean).

The concentrations of LH, progesterone, corticosterone, ACTH and thyroxine in the plasma were estimated at 2 h intervals between 10.00 and 20.00 h and at 02.00 and 06.00 h on each of the four days of the cycle. Collection of blood within 20 s of removal from the cage. Blood was collected by decapitation into chilled, plastic heparinized tubes and centrifuged immediately at 400 # and 4 °C for 10 min. The plasma was divided into portions and stored at -20 °C to await assay. Rats

were

killed

70 r

(d) 40-

'xiM

30

*v

20

10

_i_ _ _ _L.

02.00

10.00

18.00

02.00

10.00

_l_I_I_L

j_ _ _i_

18.00

02.00

10.00

0-05) from the value at 20.00 h. During pro-oestrus, the plasma concentrations of ACTH and corticosterone rose in the morning. During the afternoon they rose further and maximum concentrations of both hormones, significantly (P

Activity of the pituitary-adrenocortical system and thyroid gland during the oestrous cycle of the rat.

ACTIVITY OF THE PITUITARY-ADRENOCORTICAL SYSTEM AND THYROID GLAND DURING THE OESTROUS CYCLE OF THE RAT JULIA C. BUCKINGHAM, K.-D. D\l=O"\HLER AND CAT...
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