E. Arnon

Tamoxifen advances puberty in the White Leghorn hen.

1. Tamoxifen (TAM) administration advances puberty in cockerels. In the present study the effect of TAM administration on the sexual development of White Leghorn hens was studied. 2. Two-week-old White Leghorn females were injected intramuscularly with TAM on alternate days at doses of 0.1 mg (0.1 TM), 1 mg (1TM), 5 mg (5TM) and 10 mg/kg body weight (10TM) respectively, while the controls were injected with maize oil (vehicle). The experiment was terminated at 23 weeks of age, when all the control hens laid eggs. Sample autopsies were made on chicks of 6, 14 and 23 weeks of age. 3. Body growth was not affected by any of the treatments. 4. Comb growth was accelerated by all doses of TAM, while hematocrit increased in the 1TM, 5TM and 10TM hens. 5. Egg laying advanced in the 0.1TM and 1TM birds, was delayed in 5TM hens and did not occur at all in the 10TM females. 6. TAM caused a precocious increase in plasma oestrogen and androgen, suppressed adiposity in a dose-related manner and, at low doses, advanced the development of the gonadal system. 7. At 23 weeks of age, when the gonadal system of the controls was fully active, TAM caused a dose-related depression in abdominal fat, liver, ovary, and oviduct weights, plasma total lipids and calcium concentrations and a dose-related increase in plasma oestrogen and androgen titres, and comb weight. 8. It seems that TAM increased gonadotropic activity and its androgen stimulating action, but suppressed peripheral signs of the elevated plasma oestrogen titres. Low doses of TAM enhanced gonadotropic activity and egg laying but the antioestrogenic effect depressed development of the gonadal system, suppressing egg production when high doses were administered. It therefore seems that oestrogens are necessary for normal ovarian development in hens.

The effects of embryonic treatments with gonadal hormones on sexually dimorphic behavior of chicks

In order to study the role of sex steroids in the differentiation of chick behavior, two groups of experiments were carried out. The first part of the study documented sexual dimorphisms in three behavioral measures in chicks: open-field activity, flocking response, and masculine sexual behavior activated by testosterone (crowing, waltzing, and mating attempts). In the second part, possible organizing influences on these sexually dimorphic behaviors were examined. Male and female embryos were injected with estradiol benzoate (EB) or testosterone propionate (TP). Treatment of males with EB or TP demasculinized all three behaviors. None of the steroid treatments had any effect on the behavior of the females. Plasma testosterone levels of the chicks were not affected by any of these treatments, either before or after testosterone activation. Comb weight was reduced by treatment of male embryos with EB and increased by TP in female embryos, which suggests different mechanism for the development of somatic and behavioral characteristics. The results suggest that exogenous T or E given embryonically can exert similar effects on both sexual behavior and nonreproductive activity of chicks.

Precocious puberty in tamoxifen‐treated cockerels: Hypothalamic gonadotrophin‐releasing hormone‐I and plasma luteinising hormone, prolactin, growth hormone and testosterone

1. The administration of the anti-oestrogen, tamoxifen (TAM) to juvenile chicks results in precocious puberty. In the present study the effects of TAM administration (1 mg/kg body weight on alternate days from 12 d of age) on testicular function, hypothalamic chicken gonadotropin-releasing hormone (cGn-RH-I), plasma luteinising hormone (LH), growth hormone (GH), prolactin (PRL) and testosterone were studied in juvenile White Leghorn cockerels. 2. The increase in hypothalamic GnRH-I content which occurs during sexual development was advanced in TAM-treated birds, in association with precocious testicular development, an early rise of plasma testosterone content and enhanced comb growth. 3. Plasma LH concentrations behaved similarly and were higher in the TAM-treated than in control birds, during most of the experimental period. Plasma PRL concentration, which is high at hatching, decreased more quickly in TAM-treated than in control birds; plasma GH values were not consistently affected by TAM treatment. 4. Both the growth and the involution of the bursa of Fabricius in the TAM-treated cockerels preceded that in the control chicks. 5. It is concluded that TAM treatment induces precocious puberty in the cockerel by blocking the negative feedback action of aromatised testicular androgens on the hypothalamus.

The effect of tamoxifen on the reproductive traits in white Leghorn cockerels

Fifty White Leghorn male chicks were divided into five equal groups of ten chicks each. Beginning at two weeks of age they were injected on each alternate day as follows: corn oil as a vehicle control or 0.5, 1.0, 5.0, or 10.0 mg tamoxifen/kg/b.wt. The whole experimental period lasted until twelve weeks of age. The two lowest doses of tamoxifen (TAM) enhanced comb growth, while the highest dose suppressed it. The two lowest doses of TAM also caused an earlier increase in sexual activity of the chicks, and precocious production of semen. At nine weeks of age the 0.5 and 1.0 mg doses of TAM increased plasma testosterone to a level three times higher than in the controls. This effect was not observed with the highest dose of TAM. At 12 weeks of age the chicks treated with 1 mg TAM had larger testes than the controls and produced three times more sperm per ejaculation. At this stage chicks treated with the highest dose of tamoxifen produced less sperm than the control and had smaller testes and adenohypophyses.

Effects of bilateral basomedial hypothalamic lesions on feeding, fattiness, and reproductive functions in the White Leghorn hen

During the last three decades, syndromes caused by bilateral destruction of the basomedial hypothalamus (BMH) were extensively studied in cockerels but not in hens. In the present study bilateral electrolytic lesions in the BMH of White Leghorn (WL) hens produced two main sets of symptoms: (a) Obese, functionally castrated hen (OFC); and (b) Obese, laying hen (OL). Following the placement of the hypothalamic lesion, the OFC hens developed transient hyperphagia, that was followed by hypophagia. Weight gain was accelerated in both periods, and marked obesity developed. These hens had high hematocrit values, and atrophied ovary, oviduct, comb, and adenohypophysis. Plasma estrogen, and total lipids and liver weight were reduced in the OFC hens. In these hens, the lesioned area included the ventromedial hypothalamic nucleus (VMH), the mammillary nuclei, and in some birds also the arcuate nuclei, and the tuberal nucleus. The OL hens manifested transient hyperphagia that subsided into normophagia with the development of obesity. These hens were less obese than the OFC ones and showed normal reproductive traits. The lesioned area in the OL hens was limited to the VMH. Unlike functionally castrated cockerels, where the induced fattiness is accompanied with higher rate of lipogenesis, the OFC hen manifested a unique syndrome: increased fattiness with arrest in estrogen-dependent lipogenesis.

Sexual differentiation of copulatory behaviour in the male chick requires gonadal steroids.

1. Embryonic injections of 0.3 mg/egg of tamoxifen (TAM), 0.2 mg/egg CI-628 (both antioestrogens), 0.5 mg/egg (ATD (aromatisation inhibitor), or antibodies to oestradiol (E), all suppressed male copulatory activity (MCA) in young male chicks. 2. Embryonic injections with either flutamide (F, androgen antagonist) or high dose of antibodies to testosterone (T) only slightly suppressed MCA. 3. TAM had no effect on embryonic plasma LH levels, 24 and 48 h after injection. 4. It seems that at the embryonic stage oestradiol is required for the normal differentiation of MCA.

Effect of embryonic and neonatal administration of tamoxifen on adiposity in the broiler chicken

1. The effect of early exposure of heavy breed (HB) chicks to an anti-oestrogen (tamoxifen--TAM) on later adiposity was studied. 2. TAM administration at the embryonic stage, but not at the day of hatching, reduced adiposity in females but not in males, at 8 to 9 weeks of age. This reduction in adiposity in females minimised or even alleviated the excess of fat in females compared to males.

The response of broilers' adiposity to testosterone after embryonic exposure to androgen and tamoxifen.

1. The effects of early exposure of heavy breed (HB) chicks to an anti-oestrogen (tamoxifen--TAM) and to an androgen which cannot be aromatised (5 alpha-dihydrotestosterone--DHT) on subsequent adiposity and its response to testosterone were studied. 2. Embryonic TAM administration reduced adiposity in females but not in males at 8 weeks of age. Embryonic DHT produced similar responses but to a lesser extent. 3. Testosterone propionate (TP) administration during growth had no effect on adiposity in any of the treated groups but TP reduced adiposity in males which had been exposed to DHT at the embryonic stage.

Effect of hypothalamic electrolytic lesions in White Leghorn and broiler male cockerels

1. This study compared the effect of bilateral electrolytic lesions of the basomedial hypothalamus (HL) in broiler and White Leghorn (WL) males. 2. Hypothalamic lesions were placed in WL at 10 weeks of age (body weight 1·1 kg) and in broilers, either at 6 weeks (body weight 1·5 kg) or at 10 weeks of age (body weight 3·4 kg). They were fed ad libitum until autopsy at 16 and 17 weeks of age for broilers and WL, respectively. 3. Hypothalamic lesions caused obesity (high percentage weight of abdominal adipose tissue) in both strains. Obese fowls with unimpaired reproductive systems were classified as OB and those with functional castration as FC (functionally castrated) or FCLC (functionally castrated with large comb). 4. All post-HL syndromes—OB, FC and FCLC—were present in WL, whereas all obese broilers (which are immature at this age) were classified as OB. 5. The percentage weight of abdominal adipose tissue in OB broilers was lower than in OB WL (3% vs 5%, respectively). 6. Daily food intake of OB broilers was higher than control at 12 to 15 weeks of age, regardless of time of placement of HL, whereas daily food intake of OB WL was significantly higher than that of control WL only during the first 2 weeks following HL. 7. Body weight of OB broilers at autopsy was 20% higher than control broilers, whereas body weight of OB WL was not significantly affected. 8. An additional group of broilers was reared to sexual maturity under food restriction until 28 weeks of age. HL were placed at 10 weeks of age (body weight 1·7 kg). Autopsy was performed after a 4-week period of ad libitum feeding. 9. There were OB as well as FC and FCLC among the HL, food-restricted broilers. Percentage weight of testes and spleen were reduced in OB fowls of both strains, but more so in OB WL. 10. Hyperphagia and weight gain were not observed during the ad libitum feeding period of those obese broilers after HL, indicating that hyperphagia and weight gain are secondary to obesity.