The effect of sex steroids and hormonal contraceptives upon thymus and spleen on intact female rats

In view of a possible influence on oral contraceptives upon the immune system, the effect of chronic treatment of intact adult female rats with sex steroids and contraceptive preparations upon the thymus and the spleen was investigated. Daily injections with 10 micrograms estradiol, estradiol benzoate, or diethyl stilbestrol for 2 weeks resulted in a marked but reversible involution of the thymus, while the spleen was not affected. Androgens exerted a significant effect at a dose of 0.3 mg, and progestogens only when 2 mg were given. When various contraceptive preparations were injected for 4 weeks, there was a total involution of the thymus which persisted even 2 weeks after cessation of treatment. The effect appeared to be mainly due to the estrogenic component. Progestogens intensified the reduction of thymic weight only at higher doses. Histological examinations revealed that estrogen treatment alone resulted in a reduction of the cortex and a depletion of lymphocytes. When contraceptive preparations were administered, the medulla was also reduced, and both cortex and medulla were replaced by reticular and adipose tissue. The estrogen receptors of thymus cytosol showed dissociation constants between 0.34 and 0.49 nM in diestrous rats, progesterone-treated rats and ovariectomized rats, and binding capacities between 6.5 and 2.6 fmoles/mg protein. It remains, however, to be shown whether the estrogen-induced involution of the rat thymus may lead to an impairment of immune responses.

Serum levels and pharmacokinetics of norethisterone after ingestion of lynestrenol: its relation to dose and stage of the menstrual cycle

The peak concentration, peak time, the area under the serum concentration time curve (AUC) and half-life of serum norethisterone (NET) after a single application of lynestrenol (LYN) to female volunteers demonstrated that 0.7 mg NET is bioequivalent to 1 mg LYN which is rapidly converted to NET. There was a decrease of the peak values and an increase of half-life of NET during the periovulatory and luteal phase which was, however, not significant due to the great individual differences. The shift of the peak time to longer intervals and the increase of half-life of NET after ingestion of higher LYN doses indicate a certain limitation of the metabolic capacity of the liver. One of the volunteers who complained of nausea and vertigo after the administration of 5 mg LYN, showed the highest serum values of NET. The large interindividual variations of the serum levels of synthetic steroids demonstrate a possible risk of contraceptive safety in women with low steroid levels and possibly a coherence between extremely high serum levels of synthetic steroids and side effects.

Augmentative and inhibitory effects of chronic steroid injections on LH release and their dependency on time

The effect of daily s. c. injections of 50 micrograms ethinyl estradiol, 1 mg norethindrone and of 1 mg megestrol acetate upon basal and LH-RH-stimulated LH release was investigated in intact female rats. Basal serum LH was rapidly depressed by ethinyl estradiol and norethindrone, while megestrol acetate was less effective. the pituitary response to 30 or 150 ng LH-RH was initially augmented by the treatment with norethindrone reaching a maximum after 5 days, by ethinyl estradiol with a maximum after 10 days, and megestrol acetate after 20 days. In every case, the positive effect was followed by inhibition of H-RH mediated LH release when treatment with the respective steroid was continued. Two weeks after discontinuing of the daily injections, the blockade of the pituitary was abolished. It is concluded that a rapid decrease of endogenous LH-RH release is responsible for the suppression of basal serum LH, while a concomitant direct action on the pituitary augments the response to exogenous LH-RH during the first days of steroid application. When the treatment with steroids is continued for a prolonged period of time, the pulsatile pattern of LH-RH release from the hypothalamus becomes impaired, and this results in dependency on the type of steroid in inhibiting of pituitary response.

New aspects of the physiological significance of LRH receptors of pituitary plasma membranes

It has been found that l-cystine-bis-(4-nitroanilide), a synthetic peptidase substrate, competes with [125I]LRH for specific high affinity LRH receptors on isolated rat pituitary plasma membranes as effectively as a highly active LRH analogue. The pattern of [125I]LRH degradation by isolated pituitary plasma membranes was similar to that effected by pituitary and hypothalamic enzyme extracts. The enzyme activity seemed to accumulate in the supernatant of the membrane suspension after being released from the membrane structure.

Plasma membrane supernatant and pituitary and hypothalamic enzyme extracts were chromatographed together with labelled LRH on Sephadex G 200. This resulted in protein binding patterns with one peak at the fractions representing a molecular weight of 600 000 to 650 000 and another one of approximately 80 000, the first probably being an aggregate of the latter. After solubilization of the plasma membranes by Triton X-100, there was no evidence for another LRH receptor. There were also two peaks of [125I]LRH degrading activity (with identical metabolic pattern) and two peaks of arylamidase activity, which were, however, not identical with the binding peaks.

Both the arylamidase and the LRH binding-pattern had been demonstrated to be temperature- and hormonedependent, and seemed to be functionally related. The results indicate that there is a functional relationship between LRH binding-sites on plasma membranes and LRH degrading enzymes. This implies that the search for the 'true' LRH receptor has to be directed towards intracellular compartments of the pituitary gonadotrophs.

Hypothalamic-pituitary-testicular function in rats after supraphysiological doses of a highly active LRH analogue (buserelin)

Male pre-pubertal rats (60 g) were treated with the LRH analogue, [D-Ser(But)6]LRH(1—9)-nonapeptide-ethylamide (buserelin, Hoe 766), during 4 weeks by daily sc injections of 5, 50 or 500 ng peptide (group I, II and III). At the end of treatment, hypothalamic LRH content and arylamidase activity (LRH degrading enzyme) were not changed. Pituitary arylamidase activity was reduced, but the pituitary LRH receptors (tested by analogue binding in vitro) were not diminished. Pituitary accumulation of [125I]buserelin 60 min after iv injection was not modified and organ distribution in liver and kidney was unchanged. Pituitary responsiveness to the analogue was reduced at the highest dose, but there was significant LH-release at all three dose levels. Testosterone production in vitro (stimulated by hCG) was unaltered in group I and dramatically reduced in group II and III. Testicular testosterone content and hCG binding by testes homogenates were dose-dependently reduced. Histology of the testes after 4 weeks treatment showed minimal impairment of spermatogenesis at the highest dose, whereas the epididymis was almost devoid of sperm. The results indicate, that low dose treatment with a highly active LRH analogue, buserelin, does not interfere with pituitary responsiveness (LRH receptors and LH-release) and testicular function (testosterone production, testosterone content, LH-receptor level). At higher doses, pituitary and testicular responsiveness are dose-dependently inhibited. At the pituitary level, LRH receptors were not reduced. The antifertility effect of supraphysiological doses at the testicular level is explained by an LH-dependent loss of LH-receptors.

Ovulation inhibition by daily i.m. administration of a highly active LH-RH analog (d-ser(TBU)6-LH-RH-(1-9)-nonapeptide-ethylamide)

A highly active LH-RH-analog (D-Ser(TBU)6-LH-RH-(1-9)-nonapeptide-ethylamide = HOE 766) was administered to normally cyclic and ovulatory women in a double-blind study. Each woman received from day 1 through day 14 of the cycle according to a randomization plan either 10 microgram HOE 766 i.m. or a placebo. Ovulation was inhibited for at least two weeks in all subjects receiving HOE 766. The initially very marked release of LH measured 4 hourse after the injection decreased within 3 days by approximately 50%, and remained at this level for the remainder of the experiment while the initially high FSH response was abolished during further treatment. In 3 out of 5 women receiving the analog, serum estradiol was severely suppressed, in the remaining 2 slightly. Within 5 days after the discontinuation of treatment, the pituitary had regained the capacity to respond normally to LH-RH. It is postulated that follicular maturation is disturbed by the unphysiologic pattern of gonadotropin secretion during administration of HOE 766.

Competition of various LH--RH analogs and fragments with 135I-LH--RH for specific binding sites on isolated pituitary plasma membranes

The displacement by various LH--RH analogs and fragments of 125I-LH--RH specifically bound to plasma membranes isolated from rat anterior pituitaries was investigated. The addition of increasing amounts of unlabelled LH--RH resulted in an increasing displacement of bound 125I-LH--RH. When some fragments of LH--RH or of an analog with little biological activities were incubated, a much weaker affinity for LH--RH binding sites could be observed. No correlation between biological effectiveness and binding affinity was, however, found when several highly active LH--RH analogs were tested. The potent analogs competed much less efficiently for specific binding sites on isolated plasma membranes than LH--RH. Binding experiments with iodine-labelled (D-Ser(But)6-LH--RH(1--9)-nonapeptide-ethylamide indicated that the small binding affinity of the superactive analog may be due to a lower association rate while the dissociation rate is comparable to that of LH--RH. Contrary to LH--RH, no binding equilibrium was reached during 2 h of incubation of the analog with plasma membranes. The physiological role of LH--RH binding sites on isolated pituitary plasma membranes remains to be elucidated.

Interaction of [125I]LH-RH and other oligopeptides with plasma membranes of rat anterior pituitaries

The specific binding of [125I]LH-RH to isolated plasma membranes of rat pituitaries was investigated. The binding process was found to be highly specific, temperature-dependent and saturable. The dissociation constant as caluclated by three different methods was approximately 1.3 . 10(-8) M, indicating a single type of binding sites. Maximal binding capacity was 1 . 10(-12 moles/mg protein (= 2 ng LH-RH/pituitary gland), and the number of binding sites was calculated to be 6 . 10(11) per mg membrane protein (=1 . 10(10) binding sites/pituitary gland). When diluted with ice-cold buffer the dissociation of specifically bound LH-RH occurred very rapidly (half-life 3.17 min) with a rate constant of 0.219 min-1. The dissociation process followed first-order kinetics. Specificity of binding was demonstrated by dose-dependent competition of unlabelled LH-RH, the highly potent analogue D-glutamine-(cyclohexyl)6-LH-RH-nonapeptide-ethylamide and the fragment of an analogue (6-D-Ser(TBu))-LH-RH-(3-9)-heptapeptide-ethylamide with the binding [125I]LH-RH, while angiotensin I, II, oxytocin and bacitracin did not compete. The affinities of LH-RH and the analogue to the binding sites of the pituitary plasma membranes were not consistent with the respective biological activities.

Effect of sex hormones on HL-RH-degrading hypothalamic enzyme system during estrus cycle in rats

Basal activity of L-cysteine arylamidase, an LH-RH-degrading enzyme, was determined in the hypothalamus of rats at 4 h intervals throughout the 4-day estrus cycle. The activity of the enzyme system fluctuated during the four estrus stages in a circadian rhythm with maximal values in the night and lowest values at noon. The injection of increasing doses of estradiol-17 beta at various estrus stages caused a moderate stimulation of enzyme activity with no relationship to endogenous hormone levels or estrus stage. The highest activation of the hypothalamic enzyme in response to the application of progesterone occurred at such periods of the cycle when endogenous plasma progesterone is known to be low, and vice versa. When luteinizing hormone or prostaglandin E2 were injected i. v. during the various estrus stages maximal stimulation could be observed at diestrus. The LH-RH-degrading L-cystine arylamidase in the hypothalamus of the rat seems to play a modulating role in the regulation of the tonic LH release during the estrus cycle, but apparently does not influence the events governing the preovulatory LH-peak.

The biological activity of dimeric testosterone, a new long-acting androgen, and of testosterone enanthate in the castrated male rat

The long-term effect of single intramuscular injections of various doses of dimeric testosterone and of testosterone enanthate into castrated male rats upon serum testosterone, luteinizing hormone (LH), pituitary LH, and on the weight of the seminal vesicles, the ventral prostate and the levator ani muscle, was investigated. The effect of the enanthate was characterized by a rapid onset and a protracted androgenic action and a suppression of serum LH, while the dimeric testosterone brought about only a moderate but very even depot effect. The injection of 5 mg of the dimeric testosterone caused a positive feedback effectu upon LH release for 16 weeks. The results indicate that the dimeric testosterone may exert is hormonal effects as intact ester.

Inhibitory control of the pituitary LH secretion by LH-RH in male rats

Luteinizing hormone-releasing hormone (LH-RH) was administered to prepubertal male rats (intact, castrate or castrate-adrenalectomized, 60 g body weight) for 28 days (1 microgram LH-RH/day, s.c.), at a 10-fold physiological dose, as compared to the minimal FSH-releasing dose of 100 ng/rat s.c. In intact rats, serum LH and weight of androgen-dependent organs (vented prostate, seminal vesicles) were reduced after 14 days of treatment. In castrate rats, the postcastration rise in serum LH was abolished by treatment. Pituitary LH content, FSH secretion and prolactin secretion were not suppressed. Hypothalamic LH-RH was increased at 14 and 21 days. In castrate adrenalectomized male rats, LH secretion was also suppressed by 1 microgram LH-RH s.c. x 28 days. The hypothalamic LH-RH content did not increase. The pituitary LH-RH receptor level was not down-regulated after 14 days treatment either in intact or castrate male rats. Pituitary inhibition (LH release) in rats by a supraphysiological dose of LH-RH given for 28 days indicates that the optimal regime for chronic treatment has to be determined by monitoring LH release at regular intervals. Direct pituitary inhibition by LH-RH may explain some of the unexpected antifertility effects observed with high doses of LH-RH.

Enzyme kinetic studies and inhibition by oligopeptides of LH-RH degradation in rat hypothalamus and pituitary

The enzyme kinetic parameters of the degradation of luteinizing hormone-releasing hormone (LH-RH) and L-cystine-bis-(4-nitroanilide) (Cys-NA) by rat hypothalamic (HYP) and pituitary (PIT) extracts and the effect of various oligopeptides on the rate of LH-RH inactivation were investigated in vitro. The 105,000 x g supernatant of 1 rat HYP inactivated 57 microgram LH-RH during a 30 min incubation (Km = 12.4 microM, V max = 2.33 microgram LH-RH/mg protein/min), and of one rat anterior PIT, 48 microgram LH-RH during 30 min of incubation (Km = 12.2 microM, V max = 8.0 microgram LH-RH/mg protein/min). The synthetic substrate Cys-NA competitively inhibited LH-RH degradation with a Ki of 8.5 microM in the HYP and 6 microM in the PIT enzyme preparation. Vice versa, LH-RH also competitively inhibited the cleavage of Cys-NA with inhibition constants of 14 microM (HYP) and 15 microM (PIT) indicating that the 2 substrates are probably cleaved by the same enzyme. The most effective inhibitors of LH-RH degradation were found to be angiotensin-related peptides, neurotensin, bradykinin, and bacitracin. A relatively weak effect was obtained with oxytocin, enkephalin and puromycin. It is concluded that endogenous oligopeptides such as angiotensins, neurotensin, bradykinin, etc., may possibly influence H-RH degradation in the PIT and the HYP. The synthetic substrate Cys-NA may be an appropriate substrate for measuring the activity of an LH-RH-degrading peptidase, which therefore could be classified as arylamidase.

Time-dependent decrease of pituitary response to LH-RH after chronic treatment of intact female rats with ethinyloestradiol and norethindrone

The effect of daily injections of 50 μg ethinyloestradiol and 1 mg norethindrone upon basal and LH-RH-stimulated LH release was investigated in intact adult female rats during a period of 30 days. Basal plasma LH was depressed by about 30 % during the whole time of steroid treatment, and returned to the level of the control values two weeks after discontinuation. The injection of 30 ng and 150 ng LH-RH into untreated rats resulted in a significant increase of plasma LH which was, however, not dose-dependent. After the treatment with ethinyloestradiol and norethindrone for 5 days, the pituitary response to 150 ng was approximately four times higher than that to 30 ng. The LH release after injection of 150 ng LH-RH decreased significantly with the duration of steroid treatment, and was totally abolished by 30 days; whereas two weeks after the termination of steroid application the pituitary responded to LH-RH in the same manner as in control rats. When 30 ng LH-RH were injected into oestrogen/norethindrone treated rats, no decrease in LH release was found until day 20 of the experiment. By 30 days of treatment no rise in plasma LH could be elicited.

The activity of the LH-RH-degrading enzyme L-cystine arylamidase was stimulated during the treatment with ethinyloestradiol and norethindrone in the pituitary by approximately 100 %, whereas almost no effect on this enzyme was seen in the hypothalamus.

It is concluded that the chronic treatment of intact female rats with ethinyloestradiol and norethindrone causes time-dependent and reversible alterations in the storage of LH in the pituitary. The elevated activity of the LH-RH-degrading enzyme in the pituitary is possibly involved in these processes and/or in the mechanism responsible for the depression of basal LH.

The activity of an LH-RH-degrading enzyme in the anterior pituitary during the rat oestrus cycle and its alteration by injections of sex hormones

The basal activity of an LH-RH-degrading enzyme system, L-cystine arylamidase, was determined in the pituitary gland of female rats at 4 h intervals throughout the 4-day oestrus cycle. The activity of the enzyme was found to be fluctuating during the four stages of the cycle in a circadian rhythm with the highest values occurring at night and the lowest values at noon. The maximal activity for the whole cycle was measured at 04.00 h on the day of metoestrus, and the minimal activity between 12.00 h and 16.00 h on the day of pro-oestrus.

The iv injection of various doses of oestradiol caused only a slight change in enzyme activity of the pituitary during oestrus, but considerable increases were observed during the other three stages. The stimulation of enzyme activity by progesterone was much more pronounced during dioestrus and pro-oestrus as compared with metoestrus and oestrus. Similarly the reaction to the injection with LH and prostaglandin E2, repectively, were not very pronounced during oestrus and metoestrus, whereas the enzyme activity rose by +50% and +100%, respectively, during dioestrus and pro-oestrus.

The LH-RH-degrading enzyme system in the pituitary seems to be involved in the control of the tonic LH release, and in the maintenance and regulation of the sensitivity of the gonadotrophs to alterations in LH-RH release from the median eminence.

The regulatory function of a pituitary LH-RH-degrading enzyme system in the feedback control of gonadotrophins

It had previously been shown that a luteinizing hormone-releasing hormone (LH-RH)-inactivating enzyme in the rat hypothalamus, L-cystine arylamidase, is in all probability involved in the short-loop feedback mechanism of LH. Since this enzyme system was also shown to be present in the pituitary, the effect of the iv injection of several sex hormones upon its activity was investigated.

The basal arylamidase activity was found to be considerably higher in the neurohypophysis as compared to the adenohypophysis. The injection of 10 μg LH brought about a significant rise in arylamidase activity (+60 %) only in the latter. There was a dose-dependent increase in the pituitary enzyme activity 2 h after the iv administration of LH, and 16 h after the injection of oestradiol and progesterone into dioestrous rats.

Contrary to previous findings obtained with hypothalamic homogenates, the effect of LH upon the enzyme in the pituitary proved to be not dependent on the presence of sex steroids, as the iv application of 10 μg LH into ovariectomized rats resulted in an increase of pituitary L-cystine arylamidase by about 30 %. The injection of testosterone, oestradiol and - to a lesser degree - progesterone into adult male rats caused a significant increase of enzyme activity in the hypophysis. Progesterone proved to be ineffective in the hypothalamus.

This indicates that in contrast to the hypothalamus there is no sex-specific response of the LH-RH-degrading enzyme in the pituitary. It is concluded that this enzyme system seems to play an important part in the mechanisms regulating gonadotrophin release in the pituitary.

Acute effects of low doses of clomiphene upon LH release in ovariectomized estrogen-progesterone treated rats

The acute effects of low doses of clomiphene citrate upon serum LH within the first two hours after the intravenous injection into ovariectomized, estrogen-progesterone blocked rats were investigated. There was a short-lasting elevation of LH release 45--60 min after injection of 2.5 microng clomiphene. A second LH releasing effect occurred within 60 min when 50 microng clomiphene or more were injected. Doses between these two dose levels were not effective. It is concluded that these effects may probably be due to a partial reduction of distinct estrogen receptor sites both in the hypothalamus and in the pituitary which causes a short-lasting decrease of the negative feedback of the circulating estrogens.

Oligomeric oestradiol esters: a new class of long-acting oestrogens

Dimeric and trimeric oestradiol derivatives were administered as single subcutaneous injections into ovariectomized rats and the duration of oestrogenic effect was determined by means of daily vaginal smears. It could be shown that these preparations have a very protracted oestrogenic effect, and their threshold dose is considerably higher as compared to monomeric oestradiol diacetate. A dimeric compound containing one free hydroxy group caused a relatively even response in all animals with a linear relationship between the logarithm of dose and the duration of action. The effect was even more protracted when fully esterified dimeric or trimeric oestradiol succinates were used, but occurred in a more scattering manner. The duration of effect of 40 mug of the trimeric compound exceeded that of the equivalent dose of oestradiol undecylate. It is conceivable that the depot-effect of these oestradiol derivatives is due to delayed elimination.

A new class of long-acting hormonal steroid preparation: synthesis of dimeric androgenes coupled at C3-C3 and C17-C3 and of an androgen-progestogen combination

3beta-Hydroxy-4-androsten-17-one was prepared from 4-androsten-3,17-dione according to the method of Klimstra and Colton (1) and dimerized by means of esterification with succinic acid. The reduction with lithium-tri-t-butoxyaluminium hydride gave a testosterone derivative coupled between C3-C3 which showed after a single injection of 10 mg a protracted but relatively weak androgenic effect in castrated male rats. The direct esterification of testosterone hemisuccinate with 4-androsten-3beta, 17beta-diol gave the testosterone derivative coupled between C17-C3 which showed a more even and more protracted time response curve than testosterone enanthate. The testosterone-ethynodiol succinate also coupled between C17-C3, showed an androgenic depot-effect similar to that of the dimeric C17-C3 testosterone derivative.