Please cite this article in press as: Sharma, A., et al., Extra and intracellular calcium signaling pathway(s) differentially reg- ulate histamine-induced myometrial contractions during early and mid-pregnancy stages in buffaloes (Bubalus bubalis). Anim. Reprod. Sci. (2017), http://dx.doi.org/10.1016/j.anireprosci.2017.01.011 ARTICLE IN PRESS G Model ANIREP-5533; No. of Pages 10 Animal Reproduction Science xxx (2017) xxx–xxx Contents lists available at ScienceDirect Animal Reproduction Science journal homepage: www.elsevier.com/locate/anireprosci Extra and intracellular calcium signaling pathway(s) differentially regulate histamine-induced myometrial contractions during early and mid-pregnancy stages in buffaloes (Bubalus bubalis) Abhishek Sharma, Udayraj P. Nakade, Soumen Choudhury, Rajkumar Singh Yadav, Satish Kumar Garg ∗ Experimental Pharmacology Laboratory, Department of Pharmacology and Toxicology, College of Veterinary Science and Animal Husbandry, UP Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam Go-Anusandhan Sansthan, Mathura, U.P., 281 001, India a r t i c l e i n f o Article history: Received 8 July 2016 Received in revised form 18 January 2017 Accepted 25 January 2017 Available online xxx Keywords: Histamine Buffalo myometrium Stages of pregnancy Calcium PL-C SERCA a b s t r a c t This study examines the differential role of calcium signaling pathway(s) in histamine- induced uterotonic action during early and mid-pregnancy stages in buffaloes. Compared to mid pregnancy, tonic contraction, amplitude and mean-integral tension were signifi- cantly increased by histamine to produce myometrial contraction during early pregnancy with small effects on phasic contraction and frequency. Although uterotonic action of his- tamine during both stages of pregnancy is sensitive to nifedipine (a L-type Ca 2+ channels blocker) and NNC55-0396 (T-type Ca 2+ channels blocker), the role of extracellular calcium seems to be more significant during mid-pregnancy as in this stage histamine produced only 9.38 ± 0.96% contraction in Ca 2+ free-RLS compared to 21.60 ± 1.45% in uteri of early pregnancy stage. Intracellular calcium plays major role in histamine-induced myometrial contraction during early pregnancy as compared to mid pregnancy, as in the presence of cyclopiazonic acid (CPA) Ca 2+ -free RLS, histamine produced significantly higher contraction in myometrial strips of early-pregancy in comparison to mid-pregnancy (10.59 ± 1.58% and 3.13 ± 0.46%, respectively). In the presence of U-73122, the DRC of histamine was signifi- cantly shifted towards right with decrease in maximal effect (E max ) only in early pregnancy suggesting the predominant role of phospholipase-C (PL-C) in this stage of pregnancy. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Mast cells are the main source of endogenous histamine in the endometrium and myometrium (Massey et al., 1991; ∗ Corresponding author at: Department of Pharmacology and Toxi- cology, College of Veterinary Science and Animal Husbandry, UP Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam Go- Anusandhan Sansthan, Mathura, U.P., 281 001, India. E-mail address: profsatish@gmail.com (S.K. Garg). Pap, 2004) and the density of mast cells is significantly higher in pregnant than in non-pregnant women (Garfield et al., 2006). Quantity and activity of mast cells is influ- enced by hormonal status of the organism (Szelag et al., 2002a). Histamine is a potent uterotonic and increases contractility of isolated myometrium from pregnant and non-pregnant women (Cruz et al., 1989; Martinez-Mir et al., 1990; Rudolph et al., 1993; Castelli and Vadora, 1993), non-pregnant guinea pigs (Goyal and Verma, 1981) and pregnant and non-pregnant mice (Rudolph et al., http://dx.doi.org/10.1016/j.anireprosci.2017.01.011 0378-4320/© 2017 Elsevier B.V. All rights reserved.