Adaptation, Physiological/physiology; Insulin Resistance/physiology; Islets of Langerhans/growth & development; Islets of Langerhans/pathology; MicroRNAs/physiology; Obesity/pathology; Pregnancy/physiology; Animals; Cells, Cultured/drug effects; Cells, Cultured/metabolism; Cytokines/biosynthesis; Cytokines/genetics; Estradiol/analogs & derivatives; Estradiol/pharmacology; Estradiol/physiology; Estrogen Antagonists/pharmacology; Female; Fulvestrant; Gene Expression Regulation/physiology; Glucagon-Like Peptide 1/physiology; Glucagon-Like Peptide-1 Receptor; Islets of Langerhans/metabolism; Male; Mice; Mice, Mutant Strains; MicroRNAs/biosynthesis; MicroRNAs/genetics; Obesity/physiopathology; Organ Size/drug effects; Postpartum Period/metabolism; Pregnancy/metabolism; Rats; Rats, Wistar; Receptors, G-Protein-Coupled/agonists; Receptors, G-Protein-Coupled/biosynthesis; Receptors, G-Protein-Coupled/genetics; Receptors, Glucagon/agonists; Receptors, Glucagon/deficiency; Signal Transduction/drug effects; Signal Transduction/physiology