Hormonal status and regulation of glycemia in neonatal calves during the first hours of postnatal life

Abstract

The aim of this study was to examine changes in some hormones concentrations in calves during the first 32 hours of neonatal life and to estimate their association with glycemia. Thyrty two Holstein breed calves were selected for the study. Blood samples were taken at 30, 60 and 90 minutes postnatal. Calves received pooled colostrum: primary colostum (1.5 L, 2 hours after birth), secondary colostrum (2 L, 14 hours after birth) and tertiary colostrum (2 L, 26 hours after birth). Blood samples were taken at hours 5, 20 and 32 of neonatal life. Concentrations of glucose, insulin, cortisol, thyroid hormones and IGF-I and abundance of IGFBP-1, IGFBP-2 and IGFBP-3 were determined in the blood serum. The T3/T4 ratio was also calculated. Calves were born hypoglycemic (glycemia was 2.56±1.05 mmol/L at birth). Thereafter, glycemia significantly increased (p lt 0.001) to 3.05±0.89 mmol/L at min 90. Glucose concentration showed a further increase after colostrum intake and was significantly higher than at the initial value in all examined periods (p lt 0.001). During the first 90 minutes of neonatal life insulinemia decreased significantly (p lt 0.001) compared to initial value (26.33±10.05 μIU/L) and it measured 18.66±5.56 μIU/L at min 90. Cortisolemia was highest at minute 30 (85.08±19.36 nmol/L) and than decreased until the end of the experiment (p lt 0.001) compared to initial values in samples obtained during the period of colostrum intake. A significantly high correlation was determined between glycemia and cortisolemia in all examined periods before the first colostrums intake (r2=0.854; p lt 0.01 at min 30; r2=0.742; p lt 0.01 at min 60 and r2=0.551; p lt 0.01 at min 90). T4 concentrations significantly increased during the first 2 hours, while T3 concentrations decreased, significantly from min 30 to min 90 postnatal (p lt 0.05). T3/T4 ratio significantly increased during the first 2 hours of neonatal life. After first colostrum intake, concentrations of both hormones rose significantly compared to the initial level, but T3/T4 ratio did not change and maintained the value determined at minute 90. IGF- 1 concentrations significantly decreased during the first 2 postnatal hours. A significant positive correlation was observed between IGF-1 concentration and insulinemia (r2=0.463; p lt 0.05 at min 30, r2=0.662; p lt 0.01 at min 60 and r2=0.583; p lt 0.01 at min 90). IGFBP-3 abundance significantly decreased, while IGFBP-1 significantly increased in this period. IGFBP-2 abundance was highest at birth. Results presented in this study indicate that the increase in glucose concentration during the first 2 hours of neonatal life, before the first colostrum intake is mainly the result of increased activity of the adrenal cortex in cortisol secretion and extrathyroidal tissue thus providing sufficient triiodothyronine. Immaturity of mechanisms responsible for insulin secretion provides the dominance of catabolic processes. Changes of the IGF system provide a rise of glucose concentration and establishment of energy balance.

Cilj ovog rada je bio da se ispitaju promene koncentracije pojedinih hormona kod novorođene teladi u prvim satima neonatalnog života i utvrdi njihov uticaj na glikemiju. Odabrana su 32 novorođena teleta Holštajn rase kojima je 30, 60. i 90. minuta postnatalnog života uzeta krv. Telad su bila napajana pulovima kolostruma. Pul primarnog kolostruma davan je u količinama od po 1,5 litar 2 sata nakon rođenja, dok su pulovi sekundarnog i tercijarnog kolostruma davani 12, odnosno 24 sata kasnije, u količinama od po 2 litra. Tokom perioda kolostralnog napoja, teladi je uzorkovana krv 5, 20 i 32. sata nakon rođenja. U uzorcima krvi određ ivana je koncentracija glukoze, insulina, kortizola, tireoidnih hormona i IGF-I, kao i zastupljenost IGFBP-1, IGFBP-2 i IGFBP-3. Takođe je obračunat indeks konverzije T3 u T4. Telad su bila rođena u stanju hipoglikemije (koncentracija glukoze na rođenju je iznosila 2,56 ± 1,05 mmol/l). Nakon toga, glikemija je značajno porasla (p lt 0,001) do 3,05 ±0,89 mmol/l (90. minut). Porast koncentracije glukoze je nastavljen i nakon unosa kolostruma, tako da je glikemija u svim ispitivanim uzorcima bila značajno veća u odnosu na početnu vrednost (p lt 0,001). Tokom prvih 90 minuta neonatalnog života, koncentracija insulina se značajno smanjivala (p lt 0,001) u odnosu na početnu vrednost (26,33 ± 10,05 μIU/l) tako da je 90. minuta postnatalnog života bila 18,66 ± 5,56 μIU/l. Porast insulinemije nakon unosa kolostruma nije bio značajan u odnosu na vrednost određenu 90. minuta. Koncentracija kortizola je bila najviša 30 minuta nakon teljenja (85,08 ± 19,36 nmol/l) a zatim je opadala do kraja perioda ispitivanja i to značajno u odnosu na početnu vrednost (p lt 0,001) u uzorcima dobijenim nakon unosa kolostruma. Visoka pozitivna korelacija je utvrđena između glikemije i kortizolemije u svim ispitivanim terminima pre kolostralnog napoja (r2 = 0,854 u 30. minutu; r2 = 0,742 u 60. minutu i r2= 0,551 u 90. minutu). Koncentracija T4 je značajno rasla tokom prva dva sata neonatalnog života, dok se koncentracija T3 smanjila, značajno od 30. do 90. minuta neonatalnog života (p lt 0,05). Konverzija T3 u T4 je značajno porasla tokom prva dva sata života. Nakon unosa kolostruma, koncentracija oba tireoidna hormona se povećavala (značajno u odnosu na početnu vrednost) a indeks konverzije se nije menjao, već se zadržao na vrednosti ustanovljenoj 90. minuta života. Koncentracija IGF-1 se značajno smanjivala tokom prva 2 sata neonatalnog života. Koncentracija IGF-1 je bila u visokoj pozitivnoj korelaciji sa insulinemijom (r2= 0,463 za 30. minut, r2=0,662 za 60. minut i r2=0,583 za 90. minut). Zastupljenost IGFBP-3 se značajno smanjivala, dok se zastupljenost IGFBP-1 značajno povećavala u ovom periodu. Zastupljenost IGFBP-2 je bila najveća na rođenju. Rezultati prikazani u ovom radu ukazuju da je porast glikemije u prvim satima života, pre unosa kolostruma, prevashodno posledica pojačane aktivnosti kore nadbubrega u sekreciji kortizola i dejodinaza u ekstratireoidnim tkivima koje obezbeđuju povećanu sintezu T3. Sistemi odgovorni za sintezu insulina nisu potpuno funkcionalni u ovom periodu, omogućavajući prevagu kataboličkih u odnosu na anaboličke procese. Promene unutar IGF sistema omogućavaju porast glikemije i uspostavljanje energetske ravnoteže.