Roger A. Hoffman

Pineal Gland: Influence on Gonads of Male Hamsters

Exposure of male hamsters to cycles of 1 hour of light and 23 hours of darkness causes atrophy of the gonads. Pinealectomy prevents this atrophy, but has no effect on animals exposed to light-dark cycles of 16 : 8. Likewise, removal of both eyes induces gonad atrophy which is prevented by pinealectomy. These data emphasize the importance of the pineal gland in the regulation of photoperiodic influences on the gonads.

Effecr of light and temperature on the endocrine system of the golden hamster Mesocricetus auratus waterhouse)

Abstract 1. 1. Exposure of male hamster to short photoperiods or low temperatures for 2, 4 and 6 weeks inhibits normal increases in body weight, atrophy of the gonads characterized by increased cholesterol concentration, and by histological and histochemical appearance, and an increase in brown fat weight. 2. 2. Study of the pituitary basophils suggested abnormalities of morphology and function while massive build-up of neurosecretory material (Herring bodies) of the hypothalamus and stalk gave evidence of reduced release of this material or perhaps increased synthesis. 3. 3. The combination of short photoperiods and low temperature resulted in additive effects in terms of degree of change and rapidity of development. 4. 4. Consideration of these data in conjunction with the literature on the hamster indicates that this anima is normally a continous breeder under laboratory conditions, but a seasonal under field conditions.

Responses of some endocrine organs of female hamsters to pinealectomy and light

Abstract RECENT reports from these laboratories1,2 show that, during the winter months, normal male hamsters exposed to short daily periods of light [light:darkness (LD, in hours) = 1:23] or eyeless hamsters exposed to long periods of light (LD = 16:8) exhibit marked gonadal atrophy within 4 weeks. This effect is prevented if the animals are first pinealectomized. No significant effects are observed on weights of the adrenal gland. These studies were expanded to measure the responses of female hamsters to the two daily light cycles and to ascertain the relative influence of the pineal gland on these organs.

Influence of compensatory mechanisms and the pineal gland on dark-induced gonadal atrophy in male hamsters.

IT has been postulated that the gonads of male and female hamsters regress to a non-functional state as a normal seasonal response to short days and low temperatures in the autumn and winter1. Under laboratory conditions, the same results follow exposures to short photo-periods1–3. The functional change in the gonads is evidently controlled by the pineal gland, which itself responds to changing light periods, since pinealectomized animals show no regression of gonads when they are exposed to short photoperiods. A variable hypertrophic response of one gonad is a result of excision of the other. There are, therefore, probable hormonal processes which exert effects on the gonads opposite to those exerted by the pineal gland. In the course of our work, there arose a question as to whether the depressant action of the pineal gland could be counteracted by the compensatory process which follows unilateral castration. The following experiments were designed to elicit an answer to this question.

Harderian glands of golden hamsters: morphological and biochemical responses to thyroid hormones

SummaryManipulation of circulating levels of thyroid hormones modifies Harderian gland structure and porphyrin concentrations in male and female golden hamsters. Specifically, thyroxine (T4) and triiodothyronine (T3) induce the morphological conversion of the Harderian glands of females to approximate those of the male. Further, porphyrin concentrations are markedly decreased by this treatment. This effect occurs in ovariectomized animals as well, indicating that the gonads are not involved. Suppression of thyroid function by potassium perchlorate (KClO4) drastically reduces Harderian gland weight in both males and females. However, KClO4 decreases porphyrin levels in the Harderian glands of females and increases it in the male. Concurrently, KClO4 also induces a morphological conversion of the Harderian glands of males to the female type. This effect is evident in photoperiods of either 14:10 (h) or 8:16 (h).

Further studies on the regulation of the Harderian glands of golden hamsters by the thyroid gland

SummaryLong-term increased or decreased circulating levels of thyroid hormones significantly modify porphyrin concentrations and morphology in the Harderian glands of male and female hamsters. Administration of T3 reduced porphyrin concentrations in females; this treatment or decreasing thyroid hormone levels with KClO4 suppressed the post-castration rise of porphyrins in males. Hypophysectomy led to increased porphyrins in the Harderian glands of males; this rise was suppressed in hypophysectomized males by T3 or T4. In females, hypophysectomy reduced porphyrins which were further reduced by daily administration of T3 or T4. These modifications in the normal females were identical in castrated males. Mitotic activity in the Harderian glands of females was stimulated by KClO4 and by hypophysectomy with or without exogenous T3. In males, castration increased mitotic activity which was suppressed by T3 and exacerbated by KClO4. Increased mitotic activity seemingly follows loss of tissue mass. The data show that thyroid hormones act directly on the Harderian glands rather than indirectly through modification of TSH synthesis/release. Female “type” glands in males are a consequence of loss of gonadal androgens by castration, or by suppression or loss of thyroid hormones by hypophysectomy or by treatment with KClO4. However, male “type” glands in females are the result of androgen treatment, and/or increased levels of thyroid hormones via reduced ambient temperatures or of photic input. We conclude that regulation of the Harderian gland appears to be different in the two sexes.

Regulation of Melatonin in the Harderian Glands of Golden Hamsters

A daily rhythm in melatonin concentration in Harderian glands (HG) of female golden hamsters is described and is characterized by significant reductions following lights‐on. Concentrations in HG of intact or pinealectomized males are low and consistent over a 24‐hour period. Castration of males is accompanied by increased levels of melatonin in the HG to approach those of females. When castrated males are exposed to short photoperiods, however, melatonin levels are typically low. Levels of serotonin (5‐HT), 5‐hydroxytryptophan (5‐HTP), and 5‐hydroxyindoleacetic acid (5‐HIAA) are extremely variable in HG of both males and females, precluding definitive conclusions. Melatonin concentrations in HG of females do not appear to be affected by light or stress per se, nor are the superior cervical ganglia the pathway by which concentrations are modified.

INSULIN-LIKE GROWTH FACTOR-1 IN SYRIAN HAMSTERS : INTERACTIONS OF PHOTOPERIOD, GONADAL STEROIDS, PINEALECTOMY, AND CONTINUOUS MELATONIN TREATMENT

Abstract Four experiments in Syrian hamsters examined the role and possible interaction of photoperiod, gonadal steroids, and the pineal on circulating levels of insulinlike growth factor-1 (IGF-1). In the first experiment, female hamsters were exposed to long photoperiod (LP; 14:10 LD) or short photoperiod (SP; 8:16 LD); an additional group of SP-exposed females was pinealectomized (PX). SP induced a significant depression in IGF-1 concentrations which PX partially prevented. In Experiment 2, two groups (control and castrate [CX]) of adult male hamsters were kept in LP, and three groups (intact, CX, and CX + PX) of hamsters were kept in SP for five weeks. The four groups of animals that were CX and/or maintained in SP had approximately the same mean level of IGF-1, and all four groups were significantly (P < 0.001) higher than the LP-control hamsters. In Experiment 3, four groups (intact controls, CX, CX + melatonin pellet [MEL PEL], and MEL PEL only) were kept in LP. Melatonin pellets (1 mg melatonin/24 mg beeswax/every two weeks) were implanted sc twice during the experiment. Castration induced a rise (P < 0.001) in IGF-1 levels, and this was not prevented by MEL PEL. In Experiment 4, testosterone and dihydrotestosterone pellets implanted in LP-exposed CX males prevented the CX-induced rise in IGF-1; testosterone implants also reduced IGF-1 levels in CX males treated with progesterone. In conclusion, SP treatment depresses IGF-1 in female hamsters and raises it in males. These results substantiate previous studies in other models of gonadal steroid deficient animals. They lend further credence to the hypothesis that there is a sexual dimorphism in circulating IGF-1 concentrations in the Syrian hamster that may be at least partially related to the presence of gonadal steroids.

Interaction of harderian glands, illumination, and temperature on thyroid hormones in golden hamsters

SummaryIn this study, Harderianectomy (Hdx) has been shown to differentially modify circulating levels of the thyroid hormones, T4 and T3, in male and female golden hamsters exposed to low photic intensities or to moderately low temperatures.Specifically, low photic intensities depress circulating levels of T4 in both control and Harderianectomized (Hdx) male and female hamsters. In addition, T3 is decreased in both control and Hdx males but not in females, as a consequence of reduced levels of illumination. Moderately low temperatures (10°C) depress T4 in both control and Hdx males but not in females, while T3 is increased in both control male and female hamsters, and in Hdx males, but not Hdx females. The data suggest that the Harderian gland of males enhances the sensitivity of the TSH-thyroid axis to photic intensity and to lower temperatures, and further, that there is a considerable sexual difference in the role the Harderian glands may play in response to these two environmental factors.

Concentrations of metals in the Harderian glands of male and female hamsters

Abstract 1. 1. Harderian glands of male hamsters possess lower concentrations of Na, Mn and Ca and higher concentrations of Fe and Mo than those of females. 2. 2. Pinealectomy has little influence on metallic concentrations in these glands. 3. 3. Gonadectomy increases concentrations of Na, Cu and Mn in the male and Fe in the female and decreases Mo in the male. 4. 4. Blinding decreases Zn in both sexes and Mn in the female and increases Ca in the male and Cu and Mo in the female. 5. 5. The data strongly suggest that Mo is associated with cell type II in the male and Mn with cell type I in both males and females.