Sexual Dimorphism in Growth as Measured by Microknemometry: Different Responses to GH Deficiency and Exogenous GH Administration

Abstract

To monitor growth, a novel noninvasive leg length measurement technique, called microknemometry, which allows daily observation of tibial growth rate, was used. The rat exhibits a striking sex-related difference in postpubertal growth. Exogenous GH administration results in a sexually dimorphic response, affecting growth in normal young female rats but not in males. Here we investigated how chronic GH deficiency affects male and female rat growth patterns. The degree of growth rate recovery was investigated after exogenous GH administration to chronically deficient males and females. The deficiency was induced by neonatal monosodium glutamate (MSG) treatment. Since the neonatal gonadal environment plays an important role in the dimorphic growth pattern, neonatal androgenization of female rats with testosterone or neonatal feminization of male rats by castration was performed and the growth pattern monitored. MSG treatment decreased pituitary GH content and plasma IGF I levels in both sexes, but caused a less marked reduction of female rat tibial growth and body weight gain than in males. Additionally, only MSG-treated males showed decreased pituitary LH content, so that the dimorphic action of MSG on the gonadal axis may contribute to the observed differences in growth rate. GH administration was able to increase leg length in all MSG-treated rats but was more effective in females, despite a similar restoration of plasma IGF I levels in both sexes. Although neonatal castration of male rats resulted in a reduction of tibial growth rate and body weight, and neonatal testosterone administration to female rats caused a slight increase in body weight, a complete modification of the gender-dependent growth pattern was not achieved, indicating that appropriate steroid environment is also needed in puberty and adulthood.

Food‐Restriction Lowers the Acoustic Startle Response in both Male and Female Rats, and, in Combination with Acute Ghrelin Injection, Abolishes the Expression of Fear‐Potentiated Startle in Male Rats

“…Male rats are larger and have a much steeper growth rate than female rats ; thus, food‐restriction may be more biologically salient and discomforting in males to the point where the impetus to obtain food over‐rides danger cues. A direct comparison of the level of endogenous hunger factors, such as ghrelin and NPY, between males and females facing similar degrees of food‐restriction would address this question.…”

Recombinant human growth hormone enhances tibial growth in peripubertal female rats but not in males

“…Bone growth was measured by microknemometry (1)(2)(3)(4)(5), which is performed on conscious animals. The mean technical error of the microknemometer is about 60 mm, implying that growth can be monitored daily as this error represents approximately 10% of the rat's daily average growth, which amounts to about 550 mm/ day for a 40-day-old male rat.…”

“…A novel non-invasive leg length measuring technique, microknemometry (1)(2)(3)(4)(5), offers new possibilities when studying body growth in experimental animals. This technique allows daily measurement of tibial growth in vivo, and represents a significant improvement over other kinds of estimations of this process, such as those obtained from oxytetracycline deposition or radiographical methods which may cause damage to growth processes.…”

Sex-dimorphism in Cardiac Nutrigenomics: effect of Trans fat and/or Monosodium Glutamate consumption

“…Despite the widespread consumption of this common food flavor enhancer, which often occurs in processed and packaged foods in combination with Trans -fat, very few studies have addressed the effect of dietary Trans -fat and/or MSG consumption on cardiac gene expression. Furthermore, although sexual dimorphism at the growth hormone axis has been demonstrated in MSG-treated rodents [27], little is known about sex-specific gene expression in response to exposure to MSG.…”