Which of the following is an example of an autocrine communication?
the direct transmission of an action potential from one cardiac muscle fiber to another cardiac muscle fiber
the secretion of inhibitory neurotransmitters from a photoreceptor cell to nearby bipolar cells in the retina
smooth muscle cells secreting prostaglandins that cause contraction of the smooth muscle cells
the secretion of a thyrotropin (TSH) from the anterior pituitary gland into the blood where it travels to the cells of the thyroid gland