Seasonal changes in thyroid activity in the female sheath-tailed bat, Taphozous longimanus (Chiroptera: Emballonuridae)

Abstract

The present study was designed to investigate changes in thyroid activity during the reproductive cycle in Taphozous longimanus. Thyroid gland showed marked seasonal variation in weight and secretory activity. It was inactive in quiescence and early to mid-winter dormancy and active during recrudescence and breeding period during late winter dormancy. The serum 3,5,3'-triiodothyronine (T 3 ) and thyroxine (T 4 ) concentrations showed significant variation and closely coincided with thyroid activity. The T 3 and T 4 concentrations were higher in recrudescence, late winter dormancy and minimum in quiescence and initial stages of first pregnancy. The body weight (r = 0.56), ovary weight (r = 0.73), and thyroid weight (r = 0.70) showed correlation with each other and with T 3 and T 4 concentrations. The correlation between body weight, thyroid weight and T 3 and T 4 concentrations in non-pregnant bats was higher when compared with pregnant bats. The T 3 and T 4 levels remained low during the initial stages of development in first pregnancy when compared with the initial stages of second pregnancy. The scant food supply and low levels of T 3 and T 4 and low temperature during initial stages of first pregnancy might be responsible for differential rate of fetal development in two successive pregnancies in T. longimanus.

Secretory Processes in Follicular Cells of the Thyroid Gland of the Indian Sheath-tailed Bat, Taphozous longimanus (Hardwicke): A Ultrastructural Study

“…Similar observations are reported in hibernating and nonhibernating species of bats (Singh et al 2002, Nunez et al 1971, Kwiecinski et al 1987b, Loewenstein and Wollman 1967, Seraphim 2004) during their reproductive cycle. The most distinctive ultrastructural features in follicular cells of estrus thyroid of T. longimanus are mitochondria with lamellar cristae which are closely apposed to the elements of the rough surfaced endoplasmic reticulum.…”

“…This species of bat is continuous breeder and breeds throughout the year in Nagpur, India, (Gopalakrishna 1955). The concentration of T 3 and T 4 gradually declines towards the end of second pregnancy in T. longimanus (Singh et al 2002). Thyroid gland of T. longimanus contains large follicles lined by squamous epithelial cells with poorly defined cell organelles suggesting less active follicular cells and decline in synthesis of thyroid hormones at the end of pregnancy supporting the above observations.…”

“…At the end of gestation, large follicles are observed at the periphery of gland. Singh et al (2002) reported seasonal variation in structure of thyroid gland of T. longimanus at Varanasi, India. The species shows seasonally dioestrus breeding pattern.…”

“…Cyclical changes in the structure of the thyroid gland in Indian bats are reported in T. longimanus at Varanasi, India (Singh et al 2002) and Hipposideros lankadiva (Seraphim 2004) during different phases of the reproductive cycle. The secretory processes in the follicular cells of thyroid of bats at ultrasructural level were studied during various phases of hibernation in bats (Nunez and Becker 1970, Nunez 1971, Fujita 1971and Nunez et al 1974.…”

Thyroid Hormone Regulation and Insulin Resistance: Insights From Animals Naturally Adapted to Fasting

“…This paradoxical increase in tT4 was suggested to be physiologically regulating or contributing to important sex-related changes rather than increasing cellular metabolism (30). However, in female sheath-tailed bats (Taphozous longimanus), the thyroid gland remained inactive during early to mid-winter dormancy, becoming active during late winter dormancy, which was coupled with the breeding season (124). Last, in hibernating ground squirrels (Spermophilus richardsoni), circulating levels of TH increased, absent the availability of hepatic nuclear receptors, rendering the levels cryptically hyperthyroid (93,94).…”