TitleNutritional and hormonal modulation of insulin-like growth factor-1 with respect to growth in sexually dimorphic lizards
NameDuncan, Christine (author), John-Alder, Henry B. (chair), Cohick, Wendie S. (internal member), Carsia, Rocco V. (internal member), McCormick, Stephen D. (outside member), Rutgers University, Graduate School - New Brunswick,
Sexual dimorphism (Animals),
DescriptionIn many species of animals, adults of one sex grow faster or for a longer period of time to become larger than the other. Sex differences in growth rate can often be attributed to differences in androgenic versus estrogenic hormonal effects on the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis. In this paradigm, testosterone (T) stimulates hepatic IGF-1 message, resulting in an increase in plasma IGF-1, while estrogenic hormones have the opposite effect. However, this generality is inherently biased because studies have focused almost entirely on male-larger species. Previous work in lizards has demonstrated that T inhibits growth in female-larger species, while stimulating growth in male-larger species. Thus, the effect of T on IGF-1 may not be universal but may depend on a species’ pattern of sexual size dimorphism. Since IGF-1 had not previously been characterized in lizards, my research required the development of novel assay techniques. To this end, a partial sequence of IGF-1 was cloned. Comparison of the deduced amino acid sequences of IGF-1 confirmed high sequence identity (72 – 80%) between lizards and the corresponding region in human. These sequences supported the development of assays to characterize the response of IGF-1 to variation in food intake. In S. undulatus, zero ration decreased hepatic IGF-1 message and plasma IGF-1, while re-feeding restored levels to that of full ration. In yearling S. jarrovii, 1/3 ration had no effect on hepatic IGF-1 message compared to full ration. Altogether, results from nutritional manipulation in Sceloporus lizards are consistent with previous work but suggest that food restriction short of starvation may have little effect on IGF-1. Following the validation of assays, we investigated the effects of T on IGF-1 in a female-larger species, S. undulatus. Contrary to published studies on male-larger species, T decreased hepatic IGF-1 message in adult males and juvenile males and females. However, T did not affect plasma IGF-1. Our results challenge the widespread belief that males grow faster than females by increasing their production of IGF-1.
NoteIncludes bibliographical references
Noteby Christine A. Duncan
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.