I think you meant can I lactate without having been pregnant, since lactation is usually taken to mean producing and expressing milk following the birth of your child (I don't quite know how one would go about breastfeeding an unborn child!). In certain circumstances, it has indeed been known for women to start lactating when they haven't given birth. This is usually due to a hormonal imbalance and can be indicative of disease, such as prolactinoma, a (benign) tumour of the pituitary gland that results in increased levels of prolactrin hormone in the blood, causing stimulation of the glanular tissue in the breast to grow and produce milk secretions. So if this is occurring you should get it checked out. A baby's cry is actually at a very specific pitch and tone that causes only it's own mother to lactate (this mechanism is very poorly understood but illustrates well just how complex human physiology is). However I'm sure there have been on rare occasions occurrences of strangers lactating in response to a a baby's cry. This is probably very rare though, so if you do find yourself in this position, get it checked out as there is almost certainly a pathological reason for this.

Thank you for your answer, it was very helpful.