Impact of an acute heat shock during in vitro maturation on interleukin 6 and its associated receptor component transcripts in bovine cumulus-oocyte complexes.

Julia R Rowinski,J Lannett Edwards,Liesel G Schneider,F Neal Schrick,Louisa A Rispoli,Rebecca R Payton,Kyle J Mclean

doi:10.1590/1984-3143-ar2020-0221

Julia R Rowinski, J Lannett Edwards + Show 5 more

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https://doi.org/10.1590/1984-3143-ar2020-0221

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Journal: Animal Reproduction	Publication Date: Jan 1, 2020
Citations: 5	License type: CC BY 4.0

Affiliation: Cincinnati Zoo and Botanical Garden

Abstract

An acute heat stress event after the LH surge increased interleukin 6 (IL6) levels in the follicular fluid of the ovulatory follicle in hyperthermic cows. To examine direct consequences of a physiologically-relevant elevated temperature (41.0°C) on the cumulus-oocyte complex (COC), IL6 transcript abundance and related receptor components were evaluated throughout in vitro maturation. Heat-induced increases in IL6 were first noted at 4 hours of in vitro maturation (hIVM); peak levels occurred at 4.67 versus 6.44 hIVM for 41.0 and 38.5°C COCs, respectively (SEM = 0.23; P < 0.001). Peak IL6ST levels occurred at 6.95 versus 8.29 hIVM for 41.0 and 38.5°C, respectively (SEM = 0.23; P < 0.01). Transcript for LIF differed over time (P < 0.0001) but was not affected by 41.0°C exposure. Blastocyst development after performing IVF was not affected by 41.0°C exposure for 4 or 6 h. When limiting analysis to when IL6 was temporally produced, progesterone levels were only impacted by time and temperature (no interaction). Heat-induced shift in the temporal production of IL6 and IL6ST along with its impact on progesterone likely cooperate in heat-induced hastening of meiotic progression described by others.

Highlights

Dairy cows lose the ability to maintain body temperature when temperature-humidity index approaches 72 (Armstrong, 1994)
Noting that a major consequence of 41.0°C exposure at the beginning of maturation was to shift the temporal production of IL6 Signal Transducer (IL6ST), additional effort was put forth to examine the relative abundance of another member of the interleukin 6 (IL6) family of cytokines
IL6 levels peaked at 4.67 hours of in vitro maturation (hIVM) in cumulus-oocyte complex (COC) directly exposed to 41.0°C, whereas IL6 levels peaked at 6.44 hIVM when COCs were matured at 38.5°C (P < 0.001; Figure 2A, Table 2)

Summary

Introduction

Dairy cows lose the ability to maintain body temperature when temperature-humidity index approaches 72 (Armstrong, 1994). In moderate to severe instances of environmental heat stress, cow body temperature may reach or exceed 41.0°C (Gaalaas, 1945; Seath and Miller, 1946; Roman-Ponce et al, 1977; Turner, 1982; Elvinger et al, 1991; Ealy et al, 1993). This level of hyperthermia is problematic because for each 1°C increase in rectal temperature pregnancy rate decreases by ~25% (Ulberg and Burfening, 1967). Hyperthermia related decreases in fertility are not limited to Holstein cows but are problematic in other breeds (Dunlap and Vincent, 1971), and even Bos indicus cattle (Zakari et al, 1981)

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