家貓發身前期與發身期對葡萄糖耐受性試驗反應差異之分析

Abstract

生長激素與類胰島素生長因子為控制身體成長的胜肽類激素，尤其是在發身期階段，其影響更是重要。以人類而言，在發身期階段的兒童，與年輕成人和發身前期的兒童比較，其胰島素阻抗性會顯著性上升。本實驗的目的為比較家貓在發身前期與發身期對於靜脈注射葡萄糖耐受性試驗反應的差異，藉由分析血漿中葡萄糖、胰島素、生長激素及類胰島素生長因子第一型的濃度，以探討此差異的特性、性別的影響以及可能發生的原因。實驗貓為4隻公貓與5隻母貓，共9隻，分別於滿5月齡與滿10月齡時進行靜脈注射葡萄糖耐受性試驗。葡萄糖濃度的測定使用hexokinase glucose assay 法。胰島素與生長激素的測定，則分別使用Electrochemiluminescence immunoassay法與chemiluminescence immunoassay法。類胰島素生長因子使用ELISA法測定。本實驗葡萄糖半衰期（T1/2值）與葡萄糖轉換分率（K glucose值）的計算方式為計算15分至90分，在以10為底的半對數方格紙的線性迴歸斜率。另以梯形法計算葡萄糖與胰島素曲線下全面積。為測定胰島素敏感性，本實驗使用四種簡化胰島素敏感性測定法來定量胰島素敏感性，這四種方法分別為胰島素曲線下面積（AUCins）、homeostasis model assessment (HOMA)、quantitative insulin sensitivity check index (QUICKI) 及空腹胰島素葡萄糖比（Fasting SI1）。結果，比較發身前期與發身期組，公貓在葡萄糖半衰期（T1/2值）、葡萄糖轉換分率（Kglucose值）及葡萄糖曲線下面積，顯著高於其他各組。在胰島素敏感性變化方面，以胰島素曲線下面積（AUCins）、homeostasis model assessment ( HOMA )、quantitative insulin sensitivity check index ( QUICKI ) 及空腹胰島素葡萄糖比（Fasting SI1）這四項指數作為指標，顯示發身期公貓的胰島素敏感性，與發身期母貓及發身前期幼貓比較，有顯著性下降的情形發生。將發身前期與發身期的空腹類胰島素生長因子濃度，與AUCins、HOMA、QUICKI及Fasting SI1進行相關性分析，結果顯示發生期的類胰島素生長因子第一型（IGF-I）空腹濃度與AUCins、HOMA、QUICKI及Fasting SI1所代表的胰島素敏感性四項指數均呈正相關性，而發身前期的類胰島素生長因子第一型（IGF-I）空腹濃度與該四項指數均無相關性。因此，我們的結論是家貓在發身期也會發生如同人類兒童一樣出現胰島素敏感性下降，而發身前期與發身期在葡萄糖動力學與胰島素敏感性產生的差異與類胰島素生長因子第一型有相關性。

Growth hormone (GH) and insulin-like growth factor I (IGF-I) are important hormonal peptides affecting growth throughout the body, particularly in the pubertal period. During the time of puberty, all human children become more insulin resistance compared with prepubertal children and postpubertal youth adults. The aim of this study is to compare the difference of the response to glucose tolerance test between prepuberty and puberty by measuring the level of glucose, insulin, GH, and IGF-I in each blood sample. Four male and five female domestic cats were used in the study. An intravenous glucose tolerance test (IVGTT) was performed on each cat at 5 months old (prepuberty) and 10 months old (puberty). Blood glucose concentration was measured by hexokinase glucose assay method. Electrochemiluminescence immunoassay and chemiluminescence immunoassay was used for the determination of levels of insulin and GH, respectively. IGF-I was measured by ELISA. The Kglucose value for glucose disappearance per minute and T1/2 (half-time) were calculated by the slope of linear regression for glucose concentrations on semi-logarithmic coordinates (log10) between 15 minutes and 90 minutes. The total area under the curve for glucose (AUCglu) and insulin (AUCins) were calculated by the trapezoidal method for entire 90-minute test period. To quantify the insulin sensitivity between prepuberty and puberty, we used four simplified insulin sensitivity measurement, including area under the insulin curve (AUCins), homeostasis model assessment (HOMA), quantitative insulin sensitivity check index (QUICKI), and fasting insulin to glucose ratio (Fasting SI1), to calculate the indices of insulin sensitivity. The results of this study indicated that the T1/2, Kglucose value, and AUCglu during IVGTT were found predominently in male cats in comparison to other groups. With regard to the insulin sensitivity, it was found that the results of AUC, HOMA, QUICKI, and Fasting SI1 indices all indicate that the insulin sensitivity were significantly decreased in pubertal male cats compared with other groups. AUC, HOMA, OUICKI, and Fasting SI1 are strongly correlated with the basal level of IGF-I before IVGTT during puberty. There was no correlation between these insulin sensitivity indices and IGF-I concentration during prepubertal period. In conclusion, the decreased insulin sensitivity during puberty in domestic cats has similar characteristics as human being, and the different finding of glucose dynamic states and insulin sensitivity between prepuberty and puberty may be associated with the level of IGF-I.