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Developmental changes in levels of growth hormone mRNA in Zucker rats
I Ahmad1, A W Steggles, A J Carrillo
1Department of Anatomy, Northeastern Ohio Universities, College of Medicine, Rootstown 44272.
Abstract:
Levels of pituitary growth hormone (GH) messenger RNA (mRNA) were compared in groups of genetically obese (fa/fa) and lean (Fa/-) littermate male Zucker rats at four different ages, 3, 5, 9, and 11 weeks, in order to determine the earliest age at which a difference between the two groups could be detected. No difference was seen in three-week-old animals. Five weeks of age was the earliest time at which the level of GH mRNA was significantly decreased in the obese rats; this decrease was present at all subsequent ages. Mean serum growth hormone levels were lower in obese animals at all ages, but the differences were not statistically significant because of the large individual variation associated with the pulsatile nature of GH release. The earliest occurrence of differences in GH mRNA level is later than some of the obesity associated abnormalities present in adipose tissue. The earliest time of the GH mRNA differences can be associated with the time when decreased protein deposition is initially seen in the obese rats. Because of this association, decreased GH mRNA may enhance the development of obesity.
Insights
Growth hormone messenger RNA (mRNA) levels decrease in obese Zucker rats by five weeks of age, preceding protein deposition changes. This early reduction in growth hormone mRNA may contribute to obesity development.
Area of Science:
- Endocrinology
- Molecular Biology
- Animal Science
Background:
- Obesity is a complex metabolic disorder with multifactorial origins.
- Growth hormone (GH) plays a crucial role in metabolism and growth.
- Understanding the molecular basis of obesity in genetic models is essential.
Purpose of the Study:
- To identify the earliest age at which growth hormone (GH) messenger RNA (mRNA) levels differ between genetically obese and lean Zucker rats.
- To correlate changes in GH mRNA with other obesity-related physiological alterations.
Main Methods:
- Comparison of pituitary GH mRNA levels in male Zucker rats (fa/fa obese vs. Fa/- lean).
- Analysis conducted at four developmental ages: 3, 5, 9, and 11 weeks.
- Serum GH levels were also measured, considering their pulsatile release patterns.
Main Results:
- No significant difference in GH mRNA levels was observed at 3 weeks of age.
- A significant decrease in GH mRNA levels was detected in obese rats by 5 weeks of age, persisting thereafter.
- Serum GH levels were lower in obese rats but lacked statistical significance due to high variability.
Conclusions:
- The earliest detectable difference in GH mRNA occurs at 5 weeks in obese Zucker rats.
- This decrease in GH mRNA coincides with the onset of reduced protein deposition in obese rats.
- Reduced GH mRNA levels may be a contributing factor to the development and progression of obesity.